My reasoning is that if porn is seriously harmful and masturbation is absolutely harmless, there should be some aspect present at porn, but absent at masturbation and everyday life, which causes the harm. I have problem pointing out precisely what exactly that aspect would be.
Too much conforming to my personal taste? That's already true for masturbation. Unlike at real sex, I can decide when, how often, for how long or short time, etc. But I am supposed to believe that none of this is a superstimulus, and it cannot make real sex less enjoyable even a bit. I am also supposed to believe that the similarities between masturbation and sex will help practising and make the act easier, but the differences are absolutely inconsequential.
Seeing too many sexy ladies that I can't have sex with, some of them could be even more attractive than my partner? Well, I see sexy ladies when I walk down the street. And in the summer I will see even more. On the beach, still more. (I am not sure whether nudist beach is already beyond the limits, or not.) But I am supposed to believe that as long as I don't see their nipples or something, it is completely safe. But if I see a nipple, my brain will release the waves of dopamine and my mind will be ruined. (If I understand the definition of porn correctly, seeing a naked sexy lady on a picture is already porn, even if she is not doing anything with anyone, am I right? And even limiting oneself to that kind of porn would be already harmful.)
All of that together? So if I see a sexy lady on the beach, and then I go home and masturbate thinking about her, that's completely harmless. However, if I make a picture of her, and then at home I look at the picture, especially if the picture was taken at the nudist beach, that is harmful; the mere looking is harmful, even if I don't touch myself.
Sorry for exaggerations, but this is how those theories feel to me, when taken together. I can imagine making convincing arguments for each of them separately. I just have trouble imagining a reasonable model which would explain both of them at the same time. Why a visual superstimulus ruins the real sex, but a tactile one is completely harmless.
Compared with that, a hypothesis "it is popular to slander low-status behavior, and the rest is rationalization" seems more likely.
Honestly, dude, you seem to be sort of engaging in black-and-white thinking that I wouldn't expect from a LW reader. Yes, a noncentral example of porn use such as "looking at a candid picture of a nude woman and not touching your dick" is almost definitely harmless. A much more central example of porn use, however, is a guy who has been jacking off to porn four times a week since he was about thirteen, and has in that time seen probably hundreds of porn videos, of which he has selected a few that appeal very specifically to his particular tastes,... (read more)
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.