"But seriously, I want to keep an open mind, and I've been searching the net for the past several hours, and I haven't yet seen an intelligent, non-religious argument that's opposed to gay marriages. Anybody got any links?"
You didn't see any intelligent religious ones either, I'd wager.
"Here's another question - why are heterosexual guys generally turned on by lesbian sex (especially hot lesbians) while heterosexual women are disgusted by male homosexual sex?"
I don't know, but I would want to examine the assumptions of this question in some detail before I started looking for an answer. In the first place it could be in part a difference magnified by honesty in reporting or even a stereotypical untruth. Where is your data?