"fake geek girls" and others who try to fit in

I hate the hate on fake geek girls. Besides the obvious problem of sexism, I just don't get it.
In so many sub-cultures and interest groups there are people who insist on testing people's authenticity. Like if you don't know about the hidden track on an old album, you aren't a real fan of the band.
But think about it from the perspective of the person being questioned. If they are lying; why? What do they have to gain. I would argue friendship or at least attention. Especially in the geek culture. You aren't going to win the admiration of the mainstream, you are going to talk to people and try to make friends.
So that's why the hate really bothers me. Someone is pretending to be interested in the things you like to impress you. That's a lot nicer than making fun of you. I don't see the problem.