If its about just doing what you want to do, why are people who want to be like their friends mocked?That's something every movement has done. Thinking musically, there've been "fake rockers" and "fake punkers" and "fake rappers". In high school society there are the poser cheerleaders and the poser emo kids and the poser writers and on and on.
Hipsters mock everything. For every hipster I know, there's a great deal of cutting conversations. When I first met the group of hipsters I eventually friended, in sophomore year, I got insulted constantly and told to shut the fuck up after essentially everything I said, because I wasn't "saying the right things." Hipsters tend to always have the most comfortable niche of friends. The group I'm referring to has remained the exact same since 8th grade, adding a few people and losing practically nobody. I became "part of the group" my senior year; now I'm sitting in class next to one of those kids, and I'll likely keep in touch for a long, long time. Hipsterism is founded on diversity of interest and wit, and once those people find each other it's hard to separate them. On the flip side of that, it means they're very unwilling to expand their group, because it takes a very particular sort of person. And because their method of conversation is constantly nitpicking and criticizing, it comes across as mockery pretty easily.
"Doing what you want to do" has limitations, as does everything. It's okay to say that you cried when you read the diary of Anne Frank. It's not okay to be against homosexuality; that implies a closed mind. It's okay to be religious, not okay to be preachy about it. You can't be boring; you can't be tasteless. Taste is the tricky thing. You're allowed to be awkward, or act different from what's expected - you can cry, for instance - but you can't like bands that demonstrate tastelessness in music. (Pachebel and Nickleback are both bad.) You can't like bad movies (Plan 9 is allowed, because it's fun to watch, Mac & Me is great, but Epic Movie is a no). And while in a lot of groups taste is semi-required, in hipsterism it's all that matters.
That kinda rambled, so a summary: any hipster group is going to be closed to most outsiders, but the hipster scene is allowed to be nice and sensitive, which is a good thing.
The problem is that a lot of fakester hipsters exist, too, and it's kind of hard to tell which is which. A former friend of mine falls into the latter scene: he deliberately avoids popular music to seem edgy, insults people just to sound insulting, and wears odd clothing for no reason. The general rule of law is that if you call yourself hipster, you aren't. The people I'd call hipsters are all defined by how unhipster they are. They avoid the cliché of hipsterism. That's the point of the whole movement: you're supposed to just be yourself and do what you want, and the minute you start following trends just to be hip, you aren't. So there's where some of the mockery comes from. It's kind of like how the punks were all passionate, but their music all sounded very different. The "punk" sound really isn't. It's a washed-up, generic rip-off that ignores the rule of "be yourself." Hipsterism works the same way: the more generic it sounds, the less hip it is; the movement is about avoiding a generic center.