This might be the case for some men. I have a different theory- it's a matter of insecurity.
Do you see the men who are, for lack of a better term, blatantly heterosexual? They're the first to hit on any remotely interested-looking woman nearby, or to brag about their latest "conquest" to their friends. They're the most likely to use "gay" as a derogatory term, to loudly decry gay men as "disgusting" but lesbians (at least, most of them) "hot".
They're posturing.
It's a simple game to them- the "manliest" man wins. He wins the hot chicks (he can't imagine women being interested in anything else), he wins the adulation of all his manly friends. If you don't win, you lose, and that means being alone, without women and without friends- and the super-"manly" man can't handle that. Anything that takes away from their self-assigned "manly" score is therefore treated as the enemy, to be scorned at best and actively attacked at worst. These "manly" men can't handle the idea of even being associated with a gay man, because that's "minus points" for even tacitly accepting something so un-"manly".
So why do lesbians get a pass? They don't. Bisexual women do, and "manly" men assume that every lesbian is secretly just waiting for a "manly" man to get in on the fun. Watch how quickly a confirmed lesbian- you know, the one with no actual sexual interest in men- gets called a "dyke", and taunted for being "too ugly to score with a man" (even if said man was actively trying to get in her pants just moments ago). It's a form of cover- being denied by an attractive woman for any reason is "minus points".
Of course, there's no mainline standard for men any more than there is for women. But that's how I see a fair number of the virulent anti-gay guys as acting.
