It's the gay or GLBT community because a community has to have some kind of commonality between the individuals for what their goal is, in this case championing of glbt rights, not being scared or ashamed to be who they are. Do you think it's silly for people to be part of the competitive boggle community or linux community? I mean, why can't they just be part of the community? Oh wait they are, because you can be in multiple communities. You could easily have a gay person or a transgendered person be a part of those other two communities as well. And they are part of their local community of straight people, black people, gay people, bi people, etc.
As for the pride parades I don't have a problem with them being flamboyant and over the top because I understand how taking something you were hated for (and still hated for by many people in the GLBT's case) and show that there is nothing wrong with it, and you aren't scared or hurt by their words. It's very empowering. For all of the GLBT people who don't like the costumes and all that, you SHOULD go. The more diverse the parade the better, no? I bet if you showed up in a suit and tie and some guy dressed up as a fairy (which is of course to take away the power of calling someone a fairy, not because gay people like dressing up as fairy's all the time (though I'm sure some do)) asked why you weren't dressed up too and you said something like "Oh I'm not really into that, but I'm proud to be who I am and I am a gay/bi/lesbian/transgendered person!" I doubt you catch much or any flak. However if you said something along the lines of "how can show gay people in this light, blah blah hate hate hate" you would catch flak. Really for people who want to be accepted more, you'd think you would also be more accepting of people who seem different.
The way I see it, you are happy that you are a round peg and can fit right in, and others should strive to be a round peg too, while the pride parade people think there shouldn't be a fucking board getting in the way in the first place.