Well, speaking from my own experience, I think in many cases it does involve a certain insecurity and/or even self hate.
I would have never posted such a comment on a public message board, but I once avoided anyone who was gay or even thought may be gay for years and even in private said hateful things. The truth is I'm gay and it took me years to accept this about myself. I hated myself for being gay even! I think many of these comments are nothing but someone expressing their own internal conflicts.
Anyway, now that I've gotten to know a few gays I've discovered they're some of the warmest and friendliest people, especially my boyfriend. I was so wrong in my perceptions of the gay community! Sorry you've had to encounter this kind of hate, justaguy!