1) It sells an idea of female sexuality to boys that never turns out to be real and leaves them bitter and frustrated at women and makes genuine wonderful female characteristics seem like a cheap substitute for what all of those movies promised them.
2) It sells the idea to girls that acting like a tramp is a great way to manipulate males to get stuff from them because they are seen as brainless sex-mad freaks that will do anything for the hope of a sexual encounter. They grow to never respect good males that want a real relationship because they can always reel in another chump that will shower them with gifts by just showing some skin, instead of showing some self-respect.
I remember reading that John Stoltenberg, a self-described radical feminist man, said that pornography tells lies about women, but it tells the truth about men. He was wrong.
The truth about both men and women is that we were created to experience sexuality only in the context of marriage and parenthood. Anything else is a lie about all of us, and we know who the Father of Lies is.