Oddly enough, a lot of the stigma towards bisexual men comes from straight women. Straight women love to coo over gay men and be 'fag hags' but when it comes to bisexual men, they act like these men are covered in poo. Their two biggest complaints are "I could never be with a man who takes it up the ass" (and yet you drool over gay boys???) and "he will cheat on me with some guy, they always do!" (like a straight man can't cheat on you with some woman??) and I also see a lot of "who knows what diseases he has?" (like straight men don't have diseases??)

I've tried really hard in the past to promote bisexual men as amazing sex partners to women (a man who knows what being penetrated feels like, and what being with a man feels like, is more likely to be gentle and attentive to a woman's needs blah blah) and I've managed to convince some women to re-examine their prejudices, but it's an uphill battle. Closeted bisexual and gay men who marry women and cheat on them really ruin it for the bisexual men who just want to find one person and be monogamous.

Anyway, let me not talk on behalf of bi men, this is just my experiences watching from the outside.