My standard reaction when confronted by bigots is just a shrug. If a dog barks at you, you don't get upset; it's in his nature. When a bigot snipes at you there isn't any point trying to score points: S/he doesn't have the wit to understand you.
What to say when someone uses the "being gay goes against biology" card? All I'm looking for is a response. Not opinions about homosexuality itself.
"So how does that dovetail into the current research in neuroanatomy, psychoendocrinology, and genetics?"
My point is that "one-liners" think such statements are dispositive---so tweak their noses a little.
To my knowledge, and I could be wrong, there has not yet been found a genetic link to homosexuality, however this does not mean there is not one. The links to homosexuality have been through psychological research. They find that the people that tend towards homosexuality are not choosing, but seem predisposed from early on to be attracted to the same sex. So those using biological reasons cannot be sure, just as I'm not, but I do think it is a genitic trait, we just have not done enough research to find it.
Confuse them with ... "But laughter is the best medicine, and many people laugh when they're gay"