The idea of pornography is that it is a fantasy. Unless you attend frat parties with rap stars, I'll doubt you'll end up in a threesome with two 36-24-36 type women who will do anything you ask them. Most men (and women) understand that it is a fantasy and that they shouldn't expect it in the bedroom. But every once in a while, you can allow the fantasy into the bedroom. Say you saw a new position or technique you want to try out on a lover. Keep it open and honest and things will be ok.
What isn't healthy is when people confuse the fantasy for reality and expect all women (or men) to do all the really intense sexual stuff porn stars do. Not every woman will be down with performing oral sex, and not every guy will want to have anal sex, for example. It all depends on the person you're dating and their comfort level. Be understanding of their boundaries and know when to suggest or not suggest things to do. If you can't agree on anything sexually, than you're better off with someone else, because sex is the foundation of the relationship, and people who tell you "sex doesn't matter" are full of it. It's one of the few things we're hard wired to do as a species: go out and procreate. If we're forced to do it, might as well be good.
As for your beauty comment, the old saying "it's in the eye of the beholder" holds true. But culture does influence beauty a lot. Think of it as a single entity. Culture BELIEVES women who look like walking street lights and men who are muscle bound beyond logic are attractive because culture has changed and will always change based upon the way it reflects what it THINKS men and women want. The key is not allowing culture to influence YOU as a person in what you find attractive. I am highly attracted to what many would call "fat girls." What you see as "fat," I see curvy, volumptuous, beautiful women who might want to carry my children someday. Why do I think that? Maybe I'm a caveman, subconciously and primitively drawn to women with curves and lines and child bearing hips. Or maybe it's a genetic thing. Was my father attracted to the same thing? I don't know (nor do I want to) but these are all factors that contribute to what you think is beautiful: culture, subconcious desires, genetics, and even your own choices. No one factor should be bigger than the other, especially culture.