In a sane world, if you had a gf, you would be outraged if another man had sex with her. However, in porn, you are watching a woman that you'd have as a gf (at least if you were single) be fucked by another man, and you are getting off on her being fucked by another man or her sucking off another man. That is the definition of being a cuckold-getting off of your woman having sexual relations with another man right in your sight. At the very least, porn trains men to be cucks or to ingrain that fetish into otherwise normal men.

It also can make otherwise good young men into creepy voyeurs, which at worst, can be a crime. It instills the pleasures of watching couples have sex while they don't know you're around, turning you into some creepy "watcher," and it's normalized being a "watcher."

Even "straight" porn could be considered gay if you get excited or feel positive when you see the man's dick as he's about to plow a girl. I've heard that some gay men enjoy seeing straight men fuck women because they like seeing men in action, not caring about the woman, of course.

If you think about it, porn is kinda fucked up, at least if it isn't a nude woman or man (whatever you're into) because being nude, they're single, but porn is like a drug so a nude adult of choice wasn't enough, so they had to go into more hardcore fetishes, mirroring getting into more hardcore drugs.