I had this discussion with this uber-left person I know. This person is rabidly anti-religion, and pro-evolution (not that there is anything wrong with being either, but I wanted to point out that for this person, it's all evolution). So I asked this person, "all opinions aside, what evolutionary purpose does homoseuality serve?" The response, "you're such a homophobe," and then this person walked away.
LOL and so accurate.