This all seems to have more to do with rule consequentialism than deontology. This isn't necessarily a bad thing, and rule consequentialism has indeed been considered a halfway point between deontology and act consequentialism, but it's worth noting.
Some heuristics for identifying areas in which many thoughts are likely to have already been thought, in the form of questions: is this area of thought old? Is it important? Does it seem plausible that many smart people have thought about it before? Taking the outside view, am I in a position, whether because of historical circumstance or unusual credentials, to reasonably expect not to have the same thoughts about this issue than other smart people have had?
(Failure to use these heuristics is one way to become a crackpot.)
I sympathize. One of my professors jokes about having discovered a new optical illusion, then going to the literature and having the incredible good luck that for once nobody else discovered it first.
The thing is, to deal with any real problem, one has to work out the details. In practical application, consequentialists will have to deal with all the same facts of reality that deontologist do, and vice versa. From our last go around, I was increasingly wondering whether the difference between consequentialists and deontologists go to zero in application, and whether they're just arguing over structural commitments in their language model.
I am aware that they often come to different and stereotyped conclusions, but that could have more to do with differences in underlying moral preferences, and a failure to truly drive home to the details. My guess is we all have a bit of each in us, but prefer one or the other according to how well it facilitates our preferred conclusions.
Rule consequentliasm becomes the natural way for someone insisting on consequentialism to try to take care of deontological concerns.
They get farther by recognizing that acts are events too. What is a consequence, but an event? If you can have preferences over events, you can have preferences over acts, and you can get to have all the preferences a deontologist does, and still call yourself a consequentialist.
To reverse your last point, Sam Harris (The Moral Landscape) defends RC on the grounds that only that which is experienced can be morally significant. While agreeing, I would reply that the motivation of acts is experienced, as well as the consequences. EG: Should you vote if you live in a safe seat? You could argue that the rule "vote anyway" has beneficial consequences, but then, so does the rule "vote, except in safe seats". RC doesn't actually invent the rules, it only tells you how to evaluate them once invented! However, I would vote anyway because I wish to be the sort of person who does. (NB, I didn't say "become"). That's an example of a D-ish argument that is based on conscious experience and, it seems to me, is a valid supplement to a generally RC-based outlook.
By my understanding, rule consequentialism means choosing rules according to the utility of the expected consequences, whereas deontology argues for a duty to follow a rule for reasons which may have nothing to do with the consequences. Kant's "treat another person as an end in him/herself, not as a means to an end" doesn't mention consequences and the argument for it isn't based on assessment of consequences. Admittedly both sorts of rule may lead to the same outcome in most cases, but in totally unprecedented moral dilemmas it helps to have an idea where the rule comes from. My prejudice is that rule consequentialism is the best basis for public policy, but deontology sometimes better captures the essence of what matters in cases of private morality.
In consideration of those arguing that deontology is a kind of utilitarianism, I offer a reversal: Utilitarian ethical systems can be usefully regarded as a subset of deontological ethical systems - they're ultimately a deontological ethical system with a single rule, "Maximize utility."
Or, more accurately, "Choose the action which you think will maximize utility" (Act Consequentialism) or "Follow the rule of action that you think will maximize utility" (Rule Consequentialism). The latter is more of a meta-rule, as it leaves you to derive action rules.
While I agree with much of what you said, I think it would be better if your examples (gay marriage being good, conservativism and racism being bad) were either replaced with non-political examples or at least no longer all on the same side. e.g. if you wrote about fighting for gay marriage and against socialism, that would be more equal-opportunities political examples.
It would, of course, be different if you'd wrote "protesting about gay marriage makes me more likely to protest conservatives and racism in the future, which I don't want to do."
Forming a reputation, forming a habit, and enforcing norms are important considerations. Has anyone ever seriously tried to quantify the expected benefits and harms of these effects?
I think it's always worth mentioning here is that most of the benefit from deontology can be gained by giving the appearance of deontology. But then mentioning that one of the best ways to make others think you're deontological is to make yourself think you're deontological...
On a not particularly related note: I think one practical modern case which is pretty near deontology is the human rights agenda. I used to consider the concept of human rights fairly meaningless, but obviously it's much easier to 'objectively' challenge a government for breaching human rights than for governing in a way that ultimately leads to bad effects. And less open to abuse.
Law, in general, must be deontological. The public must be capable of predicting the behavior of legal entities, and there must be objective standards against which broaches of public functions can thus be addressed and rebuked. "Rule of law," in other words.
But then mentioning that one of the best ways to make others think you're deontological is to make yourself think you're deontological...
Or at least implement and espouse some deontological rules. You can convince yourself of these rules however you like. Once you believe that you are better off not lying, then you ought to make a deontological-style pre-commitment against lying.
This is just a test because a previous comment vanished on submission....
"So while Deontology over-corrects for this (for example, if you put a gun to my head and demand that I profess belief X, I'm going to say that I believe X, which a Deontological prohibition against lying forbids), it does so in a way that is better than many people's naive consequential thinking."
On one level, isn't all deontology consequentialist? In the deontologist moral system that proscribes lying, it doesn't proscribe saying certain words or making certain markings on paper--or to go one level higher, moving my fingers as if on a keyboard. Clearly the real prohibition is on intentionally (or through negligence) decieving someone, which is a consequence of certain acts in specific contexts.
So I think that while they seem quite different, there is a fuzzy line between the two. Of course I've no doubt this is obvious and elementary.
Well, you can think of deontology as consequentialism with infinite disutility for breaking a specific set of rules. It winds up with the same deontological rule-following, at least.
Let me preface this with an acknowledgement that Deontology has blind spots and that I'm not a Deontologist. Much like Logical Positivism, however, Deontology has good things to learn from that many Consequentialist decision algorithms miss.
Social Considerations
Your decision has consequences outside of the direct results. More specifically, if you decide to tell a lie, people are more likely to view you as a liar. This portion of consequences are easy to neglect when making a decision. So while Deontology over-corrects for this (for example, if you put a gun to my head and demand that I profess belief X, I'm going to say that I believe X, which a Deontological prohibition against lying forbids), it does so in a way that is better than many people's naive consequential thinking.
Deontological arguments are also better at convincing people that you have socially valued traits. People expect truth-tellers to tell the truth, so you want to be viewed as a truth-teller. "Lying doesn't work, so I don't lie" is a more awkward and involved argument than "lying is wrong". On a related note, Deonotological reasoning is easier for other people to model. Deontology can screen off the cost-benefit analysis that someone makes when thinking about their decisions, since all you need is the rules that they are following.
Habits and Policies
Decisions aren't made in a vacuum. They also form an implicit rule that people tend to follow. In other words, people form habits. They find it easier to do the same kinds of things that they've always done. Eating one piece of cake doesn't do measurable harm to your waistline, but having a policy of eating one piece of cake whenever you want to does.
If you're familiar with set theory, it's the distinction between {x|P(x)} and {x1, x2, x3...}. If you make decisions without consulting what policy P(x) you'd like to follow, you can make mistakes. Choosing x1 means not only having done x1, but also choosing a P(x) such that P(x1) is true.
When I sign a gay marriage petition, it doesn't just increase the chance that gay marriage gets enacted. It also makes me more likely to do other things that support the gay marriage movement, as well as make me more likely to sign worthwhile-sounding petitions in general. This is part of why I avoid social movements: trying to fight rape culture or conservatives or racism means that I'm more likely to do similar kinds of things when they don't help (Or alternatively, convince people to join whatever movement in question even when more support for that movement isn't helpful).
In short, the Deontological focus on following rules can help people enact the kinds of policies that they want to follow, even if they are bad at evaluating the value gained from following certain policies. It's a way of implementing a Schelling point, in other words - a way to choose a better policy even if breaking the policy this one time seems to work better.
Enforcing pro-social behavior
It's fairly straightforward to tell whether or not someone has crossed an arbitrary line separating pro-social and anti-social behavior. Evaluating someone's consequentialist reasoning, on the other hand, is much more difficult. Let's take, for example, the case of Christopher Dorner, the former LAPD officer who decided to expose and fight what he saw as a corrupt LAPD by declaring a personal war on them. A Deontological "don't kill cops" definitively indicts him as anti-social, whereas it's much more ambiguous whether or not trading some dead cops for a better police force is a good deal or not.
Pro-social reasons for selfish actions are also rather cheap to make or say. If you want a millionaire lifestyle, it's easy to say that your immoral business practices are for feeding starving children in Africa. It's a lot harder to say that your immoral business practices don't violate the rule "don't use immoral business practices". In general, rule-breaking is much easier to detect than utility functions you don't want to have around.