Let's not forget that bisexuality is often used as a short-hand for "evil" or "morally questionable" in a fair amount of media (most recent being in Skyfall) as that comes from, and reinforces, the idea that bisexual people are either greedy or confused. There is also classic bi-erasure which says that historically bi people haven't really been bi, they've just been trying to hide their homosexuality by romancing the opposite sex and then privately being "themselves".
Another reason to be wary of the anti-SGRA argument of "it doesn't make any sense for everyone to be bi!", or it is for me, at least.
Realistically, it doesn't make any sense for *everyone* to be bi; of course, for *some* people to be bi *does* make sense.
And that just led me to an interesting thought (though I doubt we'd see it in-game): what about bi-curious companions who ordinarily prefer one gender or the other, but are curious what it would be like with the opposite of their normal preference?