It's funny, I never really had a bad attitude about bisexual people until I spent time in the LGBT community.
I think another reason we aren't trusted in the gay and lesbian community is that by and large, the big gay organizations and their leadership are busy promoting the notion that:
"Two Mommies = Two Daddy's = A Mom and a Dad."
That is, they've decided to promote marriage equality, and pinkwashing the gay community into sort of a heteronormative / cisnormative mold.
This makes bisexuals a big problem - unless of course, you are one of the "good ones" who stick to a straight or a gay relationship. So you better "pass" as gay or straight, or they don't want to talk about you. Not at all. Also, if you are making the argument "BEING GAY IS NOT A CHOICE!!!!!!!!" then having someone who apparently does have a choice of appearing to be gay or straight is problematical. (Of course being bisexual isn't a choice at all - I'd rather be anything but this, in fact.)
They spent $300M on this one issue in this country alone last year. (As compared to $5M that was spent for all trans advocacy, education, and lobbying.) By the way - if you complain about such a disparity, most gay or lesbian people I know will be happy to rationalize away the vital importance of marriage equality to all of us, while trivializing our concerns.
So that leaves people like you "passing" as lesbian, and people like me "passing" as straight. (I am really just about 50/50 - but given that, it's just a whole lot easier to be with a guy. Unfortunately for me, I'm not one of the good ones - it's just not going to be possible to shoehorn me into anything like a heteronormative relationship. (Even the recast gay version from marriage equality.) Want me to promise to only be with my spouse, and to foreswear all others? Not going to happen. If I'm with a guy, I can promise to not be with another guy, or if I did end up with a woman as my primary relationship, I'd swear off other girls. I really hope that doesn't happen. I don't like dealing with the crap associated with lesbian relationships. Maybe if I really identified well as a lesbian, if I loved the community, if I felt at home, a real kinship around the gay and lesbian community I'd go for that. But I just do not. Don't get me wrong, I like lots of gay and lesbian folks I know, I really do. I live in the heart of the Dallas Gay community. It's been a good place for me to transition. But they just aren't my peeps.
I'll go out and celebrate marriage equality when it happens here in the US. But I'll know it's a non-event for me, and that the focus on this event pushes people like me back further into the closet. At least all things trans are becoming marketable now, and those funding machines are going to need a good cause to keep drumming up support for. Hey, maybe as trans people we'll finally get a few percent of the funding they collect, huh? That'll be worthy of a celebration, right?
So I'm queer. (There's more stuff than wanting to have sex with both a man and a woman going on. I'm really just not straight.)
I can pass pretty well for straight though, at least assuming my boyfriend can continue to deal with me and my weirdness. I don't see myself as living fulltime with a woman ever again. Been there, done that, and uh, no thanks. Now if only I weren't so attracted to women still, life would be really simple. Anyway, I already know I'm exactly what people don't want to hear about when you say the word "bisexual."
Anyway, welcome to not having a place at the table, I guess.