Due to my age and hence the G@G censorship for minors, I'm trying to be least sexual as I can be hence this take is not focused on sexual parts of porn. But irrespective of that, There are many myths about people believe in. Here are some of them:
1) BDSM Involves a Contract Agreement:

BDSM sometimes involves play contracts. These are not legal documents whatsoever. The contracts in the introduction of BDSM videos are part of the fantasy. Fantasy is that there is a “binding” document entitling one partner to the other’s body/mind/soul. Although they're used to keep track of preferences of the partner.
2) "Breaking point" of girls

(Img: Kounachi Broken Princess) This one is common among hentai watchers. It says that "If you force penetration on a woman, she'll resist it for some time ( like an hour) and then after reaching that breaking point, she'll turn into a pure slut which can do anything to get penetrated. This is a MYTH. You can't force someone for your sexual desires. It is rape. Also, breaking point doesn't exist. It is going to be painful if forced. It is just part of the fantasy.
3) Its okay to have unprotected sex

Unprotected sex is NOT okay. In porn, they do that just to make it look more real. Of course, those pornstars use birth control pills but pills can't prevent you from STDs. Always practice safe sex.
4) Porn Ruins Relationships

Yes, porn addiction can be harmful to the relationship. But in a controlled manner or watching it together can benefit your relationship.
Talking about porn may actually help couples to be more honest and accepting of one another, and get to the bottom of some other issues.
Porn can become ‘the path of least resistance,’ when couples aren’t getting along. (Dr Ari Tuckman)
5) Women Don't Watch Porn

This one is very very common among men. Women do watch porn as much as men do. There are hundreds of questions on G@G about this one! Well, women of G@G can confirm this one in comment section :)
Most Helpful Guy