[/B]I agree with you; but from what I have seen on this board there is a little more to it than a label. It seems bisexuals are often discriminated against by straights and gays because they fear the bi person leaving them for the other sex. In addition a few bad apples have ruined it for many others by being sluts and manwhores and caring little for their partners feelings.
I think there's another dynamic too, since for every person who argues that everyone's at least a little bi, there's someone else who's convinced true bisexuals don't exist. It's not just that the set of potential competition for your partner's attention doubles, but also that issues of participating in a straight or gay "lifestyle"/"scene" can affect the relationship, regardless of the two individuals in it.
I see some straight women responding negatively on the presumption they're some kind of cover of normalcy for a guy who might actually be (more|just) into dudes. On the other end, I think some gay men might worry about being abandoned for that same heteronormalcy and want to avoid guys not fully vested in a gay identity.
So, the bisexual guy gets shafted on both sides, because he's in truth neither a part of, nor "victim" to the prevailing sexual norms. I actually see some parallels here with the interpersonal affects of racial passing.
On a personal note, I've found honest-to-goodness bi guys to be very good in the sack, probably from having to negotiate both teams. But, at least for me, that's been very different, from straight-identified-turned-gay-identified dudes, who have seemed a little less... nuanced.