Bisexual men are negatively stigmatized more than any sub sect of the queer community... by straights and, often, by other gay men. It's a common assumption that bi men are untrustworthy pleasure mongers out to fuck everyone. Straight men, for their own reassurance, have to believe that bisexual women will always inevitably return to the almighty phallus after they're finished playing with each other. So, bisexual women are not such a threat.