Some comments, in no particular order:

Re: “Applying the objection to empirical and prudential claims”:

Analogizing ethical to empirical claims here only makes sense under a “naive moral realist” view of ethics. Otherwise, the notion that “morality can be any old way” (by analogy to “reality can be any old way”) is, at the least, not obvious, and possibly just stops making sense.

Re: demandingness of prudential (but also moral) claims:

“I have some terrible disease that will cause me to lose my legs if untreated, and the only available treatment for it is very expensive. But if losing my legs were very bad, that would imply that I should pay for this treatment. This is evidence that losing my legs isn’t so bad.”

There is, of course, a missing (but implied) step in this reasoning, which is something like “if something very bad is going to happen to me unless I pay for treatment, then I should pay for treatment”. This seems obvious, but if you omit it, then the reasoning no longer works, because this is the crucial connecting link between the ‘is’ of “losing my legs is very bad” and the ‘ought’ of “I should pay for this treatment”. What makes it important to notice this, is that such connecting links “screen off” the ‘is’ part of the chain of reasoning from evidence about the ‘ought’ part. In this case, the corrected reasoning goes something like this:

“I have some terrible disease that will cause me to lose my legs if untreated, and the only available treatment for it is very expensive. But if something very bad is going to happen to me unless I pay for treatment, then I should pay for treatment. Therefore, if losing my legs were very bad, that would imply that I should pay for this treatment. This is evidence that it is not the case that ‘if something is very bad for me unless I pay for treatment, then I should pay for treatment’. (It cannot be evidence that losing my legs isn’t so bad, because that’s an ‘is’ claim, screened off from evidence that bears on ‘ought’ claims by the ‘connecting link’, which is the earliest part of the chain of reasoning that can be brought into doubt by such evidence.)”

Now the reasoning is not obviously suspect. (Perhaps it is still suspect, but if so, it is only in a more subtle way.) Indeed (and unfortunately), many people in this country find themselves reasoning in just this way all the time—and, given the circumstances, I find it difficult to blame them.

Re: how to understand “demandingness objections”:

As I see it, demandingness objections are best understood as some combination of two reactions to a moral claim:

1. If you demand so much, many/most/almost-all people simply won’t do it, and a moral rule that (almost) no one follows is vacuous. (This response implicitly takes it as axiomatic that the purpose of ethics is to guide action, and if an ethical rule does not in fact work to guide anyone’s actions, then it may as well not exist.)

2. “Should implies can”. You demand more than people can do. This is a fairly straightforward intuition that ethical rules that call for impossible actions cannot be “right”. It can be extended/generalized to something like “the rightness of an ethical rule varies (in part) proportionally to how successfully it can be followed”.

In short, a “demandingness objection” to a moral claim is a response that says “people can’t and/or won’t follow the ethical rule you posit [and therefore the rule is invalid and the claim is false]”.

Re: continuity of moral claims with “caring about stuff”:

This idea does not seem to take into account second-order desires / values / etc. One perspective on ethical theories is that they are ways to systematize our values, including our higher-order values, so as to make it easier / more effective to satisfy them. On this view, I might “really care” about something, and thus “really want to” accomplish or gain that something, but on the other hand, I might also care about other things, and care about what sorts of things I care about, and whether I’m a caring person, etc., etc. A moral claim that places upon me an unlimited demand of some sort thus wouldn’t be a mere extension of caring about the things I supposedly (morally) value; it might well oppose some competing or higher-order value of mine.

I mean the complete rules that define the game.

I was very excited to look into this, but without having the rules available, there’s almost no useful feedback or commentary I can give.

Is there any reason not to share the rules as they stand? Call it a “public beta version” or something.

Due to time constraints I only want to briefly respond to this point. Do you not agree that they can suffer or do you not agree that their suffering is morally relevant?

Both. (EDIT: To clarify, I do not think that [most] animals can “suffer”, in the sense in which the word applies to a category of human experience, and also, I do not think that any of the states which are described as “suffering” by those who disagree with my assessment have, when applied to animals, any moral import.)

If you have time and are interested maybe you care to watch a few minutes of this documentary, maybe it can awaken your compassion!

This is a 2-hour-long video; I’m afraid I haven’t the time to devote to something like this (especially since watching it likely to be very low-value). If there’s some particular parts of this which you think are especially relevant, please link to them directly.

I would like to modify my original statement: The consumption of animal products is not necessary in order to be healthy. Therefore, they are unnecessary for human health. This makes their consumption optional, a choice. If you can choose non-violence over violence, I think that is a moral imperative (to which I was referring in my title).

This depends, of course, on what you define to be “violence”. If “violence” includes the killing of animals (not the usual usage, but also not unheard of)—then I disagree with the claim that choosing “non-violence” is a moral imperative.

I do not know if this holds up against your argumentation, but I would like to try anyways: I define unnecessary suffering in this case as suffering that is not essential to our lives. If the only reason we consume animal products is pleasure, the question is the following: Can we justify the suffering of others only because it gives us pleasure? As I see it not avoiding the pain and suffering of millions of animals just because we like their taste is immoral.

There are several things that might be said in response to this.

First: pleasure is essential to our lives. If you propose that we resign ourselves to living lives devoid of pleasure, then I cannot but condemn that proposal in the strongest terms. Any ideology that deems pleasure and enjoyment to be “inessential” or “unnecessary” is anti-human and, frankly, evil.

Of course, not everything can be justified by the pursuit of pleasure or enjoyment! But the question of what we may rightly sacrifice, in the service of what gains, is not a trivial one. Simply to declare that enjoyment and pleasure are “inessential” is to avoid the question, not to answer it.

Second: the question of animal “suffering”. I address this below.

Third: you say “others” (i.e., “the suffering of others”), as if it were a monolithic set, as if it made sense, morally speaking, to aggregate not only all humans, but all animals as well, or all living things, etc. But it does not—or, at least, it does not obviously make sense. Agent-neutral morality is not universally held, for one thing, and indeed some people do not include animals in their circle of moral concern at all.

Non-human animals are capable of suffering and their suffering is morally relevant. If we cannot agree on this point, I see no point in discussing the other matters further.

Ah, well. Here we come to the crux of the matter, yes? I certainly do not agree on this point!

That they are capable of suffering is not only obvious to anyone who ever witnessed some non-human animal suffer, but also scientifically proven.

Citation needed. (But before you begin collecting references, you may consider reading this recent forum thread on Data Secrets Lox, where just this topic was discussed at length.)

Not considering their suffering morally relevant is, analogous to sexism or racism, speciesism.

Labels are no substitute for arguments.

Please google the term yourself if my explanation was not sufficient.

Surely you’re not suggesting that googling the term ‘speciesism’ is going to convince anyone of anything? Do you assume that anyone who disagrees with you must simply not be aware of the term? With respect, this is not at all a reasonable assumption on Less Wrong, of all places!

Re: the Academy of Nutrition and Dietetics:

You quoted their Wikipedia page and that they profit from funding. However, according to that same Wikipedia article, they are still the largest organization of food and nutritional professionals. Every large institution needs money. They do science. Your own opinion in not trusting their science does not make their science any less credible IMO.

That they are “the largest organization of food and nutritional professionals” is irrelevant. Mere numbers of members aren’t any kind of evidence.

As for “they profit from funding”—perhaps you have missed the point, which is not that they are funded, but by whom they are funded. Do you think this does not matter? The point, to be maximally clear, is that they take money from corporations which have interests that very strongly conflict with the public interest (of getting reliable, unbiased information) and with their own stated purpose! Once again: this so-called “Academy” has severe conflicts of interest, severe enough to fatally compromise them as a source of scientific information on nutrition and diet.

Shall I quote some more from that same Wikipedia page? Let’s see:

Watchdogs note that the Academy rarely criticizes food companies, believing it to be out of fear of "biting the hand that feeds them."[67][68] Nutrition expert Marion Nestle opined that she believed that as long as the AND partners with the makers of food and beverage products, "its opinions about diet and health will never be believed [to be] independent."[63] Public health lawyer Michele Simon, who researches and writes about the food industry and food politics, has voiced similar concerns stating, "AND [is] deeply embedded with the food industry, and often communicate[s] messaging that is industry friendly."[69]

You would trust this organization, when these experts do not? What do you know that they don’t?

A 2011 survey, found that 80% of Academy members are critical of the Academy's position. They believe that the Academy is endorsing corporate sponsors and their products when it allows their sponsorship.[70]

You would trust this organization, when four out of five of their own members do not?

The organization also publishes nutrition facts sheets for the general public, which food companies pay $20,000 to take part in writing the documents.[73] A list of these publications for the general public include: […] This industry funding also gives food companies the ability to offer official educational seminars to teach dietitians how to advise their clients in a way that advances the interests of the food company. For instance, in a Coca-Cola sponsored seminar for dietitians, the speaker promoted free sugars consumption for children as a healthy choice.[79]

To be frank, the idea that the Academy of Nutrition and Dietetics is a reliable and unbiased source of nutrition-related information is ludicrous. To claim otherwise undermines the credibility of every other claim you make.

However, here is a further source that links to several other organizations that have affirmed that vegan diets are healthy:

https://www.veganism.com/is-vegan-diet-healthy/

I hope that addresses argument (1) sufficiently.

By no means does this address the argument at all.

You have linked to an advocacy website. Not to a meta-analysis or review, not to a paper published in a respected journal, not even to a popular science article in a reputable publication, or a blog post by a scientist working in the field—but to an advocacy website. I’m sorry to be blunt about this, but—do you not see how worthless this is, as evidence? (And lest you consider replying that they link to other, more reputable sources, recall that a biased advocate for a position can cherry-pick sources to support almost any possible point—see “What Evidence Filtered Evidence?” and “The Bottom Line” for further commentary.) Linking to a page on a vegan advocacy site and declaring the matter settled is simply not anything even resembling a serious approach to this topic.

Suppose I were interested in investigating this topic for myself. Setting aside the deep skepticism which it is only rational to cultivate about any nutrition-related topic, and the awareness that advocacy of all sorts, and profound systemic and instutional flaws, compromise the reliability of even credentialed sources, I might do the maximally naive thing and simply do a web search for “vegan diet health”. On the very first page of search results, I would see sites and documents which say things like:

One common concern is whether a vegan diet provides enough vitamin B12. B12 helps prevent nerve damage, and is found in meat, fish, eggs and dairy, but not in fruit or vegetables. It's recommended that adults consume 1.5 micrograms of the vitamin per day.

“A B12 deficiency can lead to neurological symptoms such as numbness, and it’s irreversible if the deficiency is present for too long,” says Janet Cade, of the Nutritional Epidemiology Group, School of Food Science and Nutrition.

A recent study involving 48,000 people over 18 years compared the health of meat-eaters, pescatarians – who eat fish and dairy but not meat – and vegetarians, including some vegans. They found that people who eat vegan and vegetarian diets have a lower risk of heart disease, but a higher risk of stroke, possibly partly due to a lack of B12.

Researchers are concerned that a lot of research comparing the vegan diet and health outcomes (also known as observational research) is unreliable, since vegans tend to be healthier.

“Typically, vegans smoke less, drink less alcohol and exercise more,” says Faidon Magkos, associate professor at the University of Copenhagen's department of nutrition, exercise and sports, who last year published a review into research examining the health effects of the vegan diet.

These lifestyle factors, which can also contribute to a lower risk of heart disease and mortality, can suggest that the vegan diet alone is healthier than it may actually be.

While the evidence isn’t very strong for the vegan diet specifically, Cade says, the vegan diet seems to be linked to better general health, apart from bone density and fractures, which may be more common due to possible lower calcium intake, and the likelihood of B12 deficiency.

“If you compare a plant-based diet with an unhealthy diet that includes meat, the plant-based diet is certainly better,” Faidon says.

“But if you follow a relatively prudent omnivorous diet, such as the Mediterranean diet, which is high in fruit, vegetables, legumes and low in meat, there’s evidence to suggest this type of omnivorous diet is at least as healthy as a vegan diet,” he says.

(From https://www.bbc.com/future/article/20200122-are-there-health-benefits-to-going-vegan)

(See also https://empoweredsustenance.com/is-vegan-healthy/ for a laundry list of other concerns.)

At the very least, this would convince me that the case is far from closed, and that much more investigation is needed.

EDIT:

I think you should not underestimate nutritional science and do your research first if you make such a claim. The scientific findings are sufficient to claim that vegan diets are healthy. Therefore, humans do not need animal products to be healthy.

Citation needed. Since you suggest that I do my research, no doubt you’ve done yours—yes? The “scientific findings” you refer to ought to be cited explicitly.

(Continuing from my other comment.)

[stuff about world hunger]

Another commenter has already addressed this somewhat, but to make the point explicit: as you say, we produce enough food already. Hunger in the modern world is caused by logistical difficulties, not under-supply. There does not seem to be any reason to believe that a global transition to veganism would meaningfully affect these difficulties. (This is to say nothing of the highly questionable implied connection between personal decisions, made by individuals in Western countries, to adopt veganism, and any significant shifts in global prevalence of veganism.)

Being vegan contributes to saving wild animals

This point is rather at odds with your argument about animal welfare. The lives of wild animals are full of pain and death—a fact which has long been recognized by effective altruists. (Simply search for “wild animals” on the Effective Altruism Forum to get a flavor of the discussions on this topic.) If you want to reduce unnecessary suffering, are you sure you should be saving wild animals?

Vegans are overall healthier, are less overweight, have less cancer (at least some forms of cancer like breast or prostate cancer), and have fewer cardiovascular diseases, including strokes and heart attacks.

Citation very much needed. (And see the note in my other comment about health-related claims.) My prior for this sort of claim (taken as a universal or near-universal claim, which is the only way it can have any rhetorical force) is very low.

Invalid arguments against being vegan: …

The “natural“ and “normal” arguments are indeed mostly invalid (though there are serious “Chesterton’s fence” type concerns which ought not be casually dismissed). The “necessary” argument is certainly not invalid (or, rather, requires considerably more support than the almost no support which you have provided, in order to be rejected as invalid).

the Academy of Nutrition and Dietetics

I looked them up and found this:

A 1995 report, noted the Academy received funding from companies like McDonald's, PepsiCo, The Coca-Cola Company, Sara Lee, Abbott Nutrition, General Mills, Kellogg's, Mars, McNeil Nutritionals, SOYJOY, Truvia, Unilever, and The Sugar Association as corporate sponsorship.[25][61] The Academy also partners with ConAgra Foods, which produces Orville Redenbacker, Slim Jims, Hunt's Ketchup, SnackPacks, and Hebrew National hot dogs, to maintain the American Dietetic Association/ConAgra Foods Home Food Safety...It's in Your Hands program.[62] Additionally, the Academy earns revenue from corporations by selling space at its booth during conventions, doing this for soft drinks and candy makers.[25][63]

(From Wikipedia. Click the link for more in the same vein as the quoted paragraph—there’s a lot there, and all of it bad.)

Under no circumstances would I believe a word these people say about nutrition.

Tradition, taste, convenience: The holy trinity of lazy excuses. Neither the tradition of eating meat nor the taste or convenience of it are able to justify the unnecessary suffering of sentient beings from a moral perspective.

These are, in fact, entirely valid reasons to eat meat—especially if the moral argument fails to persuade. Far from being “lazy excuses”, these three considerations are quite important to the great majority of people! It is empirically true that people value tradition, taste (or, more generally, pleasure and enjoyment), and convenience very highly. (If you doubt this, look at the choices people make!) The task before you is daunting: you must convince people, not only that eating animals (or harming them in the process of food production) is wrong at all, in any way, but also that it’s wrong enough to outweigh things that they actually, in fact, value quite highly.

(And, of course, if the moral argument doesn’t hold water—as I, for one, don’t think it even slightly does—then the point is moot. What reason suffices to justify doing something that’s morally neutral? Why, any reason at all.)

And now, a substantive reply.

Well, as you say, the post is very sloppy, which makes me feel somewhat bad for arguing against it… but if no one speaks up to point out shoddy argument, on a topic of concern to us, then it’s normalized, isn’t it? If you like, consider my commentary to be aimed, not (only) at you per se, but at anyone who makes similar arguments (of whom there are many).

Animal welfare: Humans do not need animal products to be healthy. Therefore, the consumption of animal products is unnecessary. This makes the killing of non-human animals for animal products unnecessary. Not avoiding unnecessary suffering is immoral. Therefore, contributing to unnecessary animal suffering makes you an animal abuser.

This is a series of claims stringed together—almost all of them either unsupported or wrong. Let’s look at them individually. I will number the claims for convenience.

(1) Humans do not need animal products to be healthy.

Citation needed. When providing citations, please note that (a) much of nutrition science is very shoddy (in all the usual ways—methodology, replicability, file-drawer effects, etc.), and (b) there is considerable variation, between people and between groups of people, in optimal diet, physiological responses to dietary changes, etc. Almost any universal statement about human nutrition is likely to be wrong. So a claim like this requires considerable support to be raised even to the “plausible” level, much less to “certain enough to base moral claims on”. (Indeed, it is possible that nutrition science, in its current state, is simply not capable of providing us with the degree of certainty which we would need in order to use a claim like this in a moral argument.)

(2) Therefore, the consumption of animal products is unnecessary.

Granting claim (1), this one does not follow. You seem to imply that something is only “necessary” if, without it, we would die (or suffer serious harms to health). I reject this view.

(3) This makes the killing of non-human animals for animal products unnecessary.

Note that if your argument depends on establishing the immorality of killing animals, that gets you to vegetarianism only, not to veganism. Eggs, dairy, etc. do not require killing animals, so a non-vegan vegetarian might well ask—how does this argument apply to me?

(4) Not avoiding unnecessary suffering is immoral.

The word “unnecessary” seems to be doing most of the work in this claim, but it’s difficult to see how to operationalize it. Interestingly, utilitarianism (which is usually a background assumption in arguments like this, and likely here as well, though you never name it explicitly) doesn’t much help; there isn’t really any way, for a utilitarian, to designate some suffering to be “necessary” or “not necessary”—it simply gets entered as input into the utility calculation, along with all other relevant facts about the world. On the other hand, most non-utilitarian views don’t offer any clear way to make sense of this claim either.

(5) Therefore, contributing to unnecessary animal suffering makes you an animal abuser.

This presupposes several other claims, which are missing from your argument, and must be made explicit. These include “non-human animals are capable of suffering” (and/or “the suffering of non-human animals is morally relevant”).

As a side note, the term “abuser” is tendentious; clearly, you are trying to bring in the connotations of the term we use to describe people who beat their pet dogs, into the argument about whether it’s acceptable to kill cows for their meat. If you have a point, make it without recourse to underhanded emotional tactics.

(The rest of the paragraph is mostly elaboration on claim (5); the factual claims made therein are irrelevant if the argument quoted above does not carry through.)

(Continued in sibling comment, for ease of response.)