There is a scene in Shakespeare's Julius Caesar in which the protagonist, in his discomfiture over his wife's barrenness, embarrasses her in front of a crowd. He suggests that she perform a superstition in order that she might become fertile. But he also embarrassed himself in a way, for he could rule everything except biology. We, too, want to rule our biology, be it via gay marriage or gender roles or our genetic tendencies.
I don't understand why it matters whether it's "nature" or "nurture" with respect to how someone becomes gay. Is it any less unfair if, perhaps due to a bad or weak father, someone "becomes" gay? Is it the gay person's fault they are gay? Usually not. If it's "nature", does that mean God made them that way and they can do what they will? Some ethnic groups are genetically disposted to alcoholism - does that mean God doesn't mind if they're always drunk?