It's complicated, especially for bi people who ARE strongly/mostly same-sex attracted. Like when I first came out as bi, I was "welcomed" into the community by people talking about how bisexual women were disease carriers and tainted by men even though I'd never even been with a man at that point. I also asked some people point blank if I should just ID as lesbian and they told me yes -- and I was treated better once I did. I've gained a bit more self-worth since then (and decided anyone who can't accept me for who I really am isn't worth the trouble, especially not as a potential romantic partner), but that sort of thing leaves an impression. While I see the problems it can cause, I also understand why some bi people who are strongly same-sex attracted might find it easier just to call themselves gay/lesbian to blend in.

As for the ones who are, say, already in monogamous straight marriages (and never showed a hint of being anything but straight), but can't shut up about how ~QUEER~ they are.... Well, I know it's not my fault, but I'm still very sorry and don't personally claim them. :p