I felt that what Englishman said kinda summed up my reasons, but I should personalize it a bit.
I left two decades ago, when everyone else that I knew was in and considered me a lost sheep. For a long time i was content to pretend that I was, This was made easier by the fact that my frequent honest statements of (dis)belief were met with incredulity by those who really wished I'd "straighten out." they didn't want to hear; they couldn't hear; and I didn't want to SHOUT. I'm hoping that some other person a bit like me may come here and I be able to express soemthing that helps them.
I'm also here because I am angry; angry for myself and all the other kids I grew up with who are now dysfunctional adults in one or more ways. I savor each expression of independence from the Borg that I read, wishing that I might see the collapse of this foul false prophet, but knowing that I probably will not.
I'm here to mock spiritual insanity, to reveal absurdity by being even more absurd.
There are some here for whom I feel great admiration, male, female, straight, gay, atheist or heart-felt christian; but none with whom I've yet developed any friendship. Lack of socialization skills, you might call it. I spent all of my formative years being the good witness kid, avoiding everything and everyone that didn't have the WTBTS imprimatur on it; still I was never really good enough for THEM, either. I *know* I'm different, you see; I *know* you wouldn't like me. I don't really like myself.
...and I'm here for the chicks!