One can imagine all kinds of confounding effects, where some other thing makes someone more likely to use porn, and also is (or causes) something else that is good or bad.  And the confounding effects are likely to be different in different subpopulations (e.g. young university kids; people who were raised religious and might not be anymore; people in relationships, some of which are going better than others; old people, some of whom are losing their sex drive).  So I would put very little trust in any study that didn't involve a randomized intervention.  (Which isn't a guarantee of quality—it's only one dimension.)  And I think there are plenty of people making claims based on ... well, let's just say their standards for empirical rigor are much lower than mine.

Wiki has an article, which is somewhat interesting to look through.  This is a bit hilarious coming after the above:

Studies have looked into both negative effects of pornography as well as potential benefits or positive effects of pornography. A large percentage of studies suffer from methodological issues. In one meta-study by researchers at Middlesex University in England, over 40,000 papers and articles were submitted to the team for review: 276 or 0.69% were suitable for consideration due to the low quality of research within the field.

It could be worth looking into those 276, but I'm not going to do so before posting this comment.  (Also I wouldn't be surprised if many of those were bad for reasons the researchers didn't catch.)  So, um, I think we're left with armchair theorizing and amateur observation.  Let's see.

Ways it could go wrong:

• There are apparently people who get addicted to porn, so maybe it's harmful for them.  On the other hand, I think people who get addicted to things often have bad stuff happening in their life already.^[1]  On the first hand, even if the addiction is caused by bad stuff, it's possible that the addictive behavior makes the situation worse.  On the second hand, if you were going to be addicted to something, porn is probably way less bad than, say, drugs or gambling.
• Obviously, porn has its realistic and its unrealistic elements, and people who can't tell the difference and don't know it are likely to do ill-advised things.
• For some, the usage of porn has baggage because of an upbringing that thought it (or perhaps masturbation or sex more generally) was shameful, or because other people in their life have opinions about their porn usage, or it connects to relationship problems (e.g. the partners have differing sex drives, or one wants a type of sex the other is unwilling to do, and uses masturbation with porn to compensate).  Recommendations there would be situation-specific, although in general I'd say these situations already have a conflict, and the other option (i.e. abstaining from porn, or masturbation in general) may carry its own downsides (frustration, resentment) and isn't necessarily better.
• I've seen claims that some people get bored with "vanilla" porn, check out something a little spicier, get bored, etc., and end up in pretty extreme places.  I'm sure this has happened.  I don't think it's common.  I also suspect that those people had an underlying tendency and many of them would have arrived at similar places via in-person sex, if their environment made this easy (and would have been frustrated, and done who knows what else, if their environment did not).

Ways it could go well:

• Obviously, people find it pleasurable or otherwise rewarding.
• If one's sex drive would otherwise lead one to do unsafe, immoral, or otherwise bad things, this may be a better alternative.  (To some extent one can say this about masturbation regardless of whether it involves porn.)
• If one wants to expand the range of, say, body types or demographics one is interested in, porn is an easy way to explore that.

There is plenty of speculation about long-term effects, habit forming, and so on.  (I personally look out for the possibility of becoming dependent on porn, and make a point of masturbating using only my imagination reasonably frequently.)  I don't think there are large effects that reliably happen, otherwise I'd probably have heard about it.  (There's a whole "No Fap" movement that some subscribe to.  I think some people claim it improves their motivation / energy.)  Probably, if there are such effects, they affect some people much more than others.

Overall, I'd say "seems probably harmless; it's probably worth having some awareness of failure modes and paying attention to yourself, but beyond that, do what thou wilt".

1. ^{^}

   Valentine had an interesting post where he said "This is the basic core of addiction. Addictions are when there's an intolerable sensation but you find a way to bear its presence without addressing its cause. The more that distraction becomes a habit, the more that's the thing you automatically turn to when the sensation arises."  The idea of being addicted to escape from a thing you're avoiding, rather than being particularly addicted to the specific form of escape, rings true to me.

I think it's a complex question. For example, people debate whether porn is harmful or helpful:

• Morally or practically
• In the short vs. long term
• To the actors
• Directly to the viewer
• To the viewer's partner
• To culture as a whole
• For intrinsict reasons or because of how it intersects with the rest of our culture
• Universally, on average, or in specific circumstances
• Whether it's actually harmful/helpful or just a suboptimal/better way to express sexuality

If you get specific enough about these questions, it may be possible to ask meaningful scientific or moral questions. When I've seen debates over porn seem productive, it is usually because the participants have stopped generalizing and tried to get really specific on what exact question they're asking, why, and how.

But this in turn poses a new problem: how would you figure out which bits of this debate are relevant to you? And once you have an answer to this question, you may find that there really isn't much reliable information out there that's pertinent to you.

But if you just want to trawl through the scientific literature, I would just approach it with the same open-minded skepticism you'd bring to any other such project.

Seems like the consensus is that there is no consensus, only many people with strong opinions either way.

Perhaps the question is underspecified, and we need to ask more precisely: what kind of porn? for whom? how often? compared to what alternative? harmful for whom? (etc., see DirectedEvolution's answer).

Now of course this sounds like a fully general counterargument -- we can deflect any inconvenient question by asking endlessly (are apples healthy? -- what kind of apples? for whom? how many? compared to what?), but with apples, we can assume some reasonable defaults, like "the kind of apples you can buy in a supermarket, or grow in your garden" and "somewhere between one apple a week and ten apples a day", and within this range the answers will probably be quite similar.

With porn, the range is probably much wider. Frequency, from "a magazine hidden under my bed, which I browse once in a month", to "I am an unemployed guy and I spend 16 hours a day watching porn online". The kind of porn, from mere uncovered boobs, or the kind of vanilla sex that your Pope would approve of, to the most depraved shit that would leave an average person traumatized for the rest of their lives. Is watching porn a part of a balanced lifestyle that also includes seeing real people occasionally; or a way to overcome solitude during your climb to the top of Mt. Everest; or a neurotic distraction while you procrastinate on filing your tax reports?

Arguments in favor of porn:

• some people like it;
• under some hypothetical, extremely rare circumstances that practically never happen in real life, carefully selected porn could serve as a form of sex education;
• for perverts who are turned on by horrible things, watching porn is a socially preferable alternative to actually doing horrible things in real life;
• no one gets pregnant from watching porn;
• people can find inspiration that will enrich their sexual lives;
• watching porn together with your partner can be a form of foreplay.

Arguments against porn:

• it makes Jesus cry;
• it makes you objectify people, and that's wrong;
• general objection against superstimuli (you can see more attractive people naked during one evening than your ancestors could see naked or clothed during their entire lifetime, isn't that amazing?);
• if you spend too much time -- you should be doing something useful instead;
• seeing too many too attractive people may set one's bar unrealistically high;
• and vice versa, people can be afraid that porn sets other people's bars too high;
• seeing too much too soon can make people scared of actually trying sex (afraid that their partners would expect things they are not comfortable with);
• people may not realize that average porn is not representative of average sex (things that look best on screen are not necessarily the things that feel best in real life; perverts are better customers than normies, therefore their preferences are overrepresented);
• people saturated with porn may be less motivated to find partners in real life, or may neglect their existing partners;
• multiply the changes in individual behavior by millions, and you get social changes (fewer marriages? fewer kids?);
• sometimes porn is produced unethically (people coerced into performing);
• masturbating while watching porn makes you lose precious bodily fluids.

Now good luck putting this all into one equation!

The underlying issue here is that the supply of sex, quality of sex, supply of quality partners and the logistics of all the above cannot meet the popular demand. It would require the number of highly libidinous attractive partners to be equal or exceeding the number of adults that desire sex. Until we somehow achieve Sexual Post-Scarcity (how? Sex-bots? VR sex? Massively orgiastic global swinger culture?) then porn is unavoidable.

Good sex with an attractive partner is an extremely scarce resource. In fact, any sex, even crappy one, is scarce, and far, far below popular demand. Porn is a necessary plug. It provides a better form of sexual release than pornless masturbation.

So in that regard, it is obvious that porn is more beneficial than harmful, since the alternative to porn for many is effectively celibacy, which has plenty of harmful psychological and social effects, including violence (sexual and otherwise).

 

very simple. porn is pleasure to make and consume, therefore good. the end

(how to simplify your life with hedonism, s0ph1a 2012-∞)

The consensus is don't ask, don't tell. It's the only media consumption (among movies, tv, books, sports, videos, music, games etc.) that's not openly discussed around the water cooler or in polite society. A disservice, in my opinion.

It appears to be harmful to children because it takes time away from other activities and creates false impressions of sex/relationships. Especially if porn is their only reference for adult relationships. Children younger than 16 should be educated on media (including porn) but probably shouldn't have free reign to explore porn content as it may consume their whole life. 

There's also an escalation effect where users will seek out increasingly hardcore content and become so desensitized to pornographic content that they have no physical reaction to real world relations (I assume the 2019 pubmed article that was linked discusses this effect). How harmful it is, and how we know, are open questions which are hard to study because it's a taboo subject and because it's difficult to decouple porn from other screen based consumption. For example, we may have strong data with proper testing methods that definitively proves the harms of porn and then still wonder is it necessarily more harmful than YouTube or Netflix?

When I think about porn on net being good or bad, I think, what are characteristics of societies which exist in the world today that ban porn? What are the characteristics of the societies which have a lax, open attitude towards it?