147: If people are gay biologically, then the two participants in successful, happy marriages are just two more straight people getting married who would’ve gotten married anyway. (Okay, so it’s probably possible for a gay man to happily marry a woman, but as a countermeasure I wouldn’t count on it.)
Believe it or not, just because gay marriage is legal doesn’t mean that men aren’t marrying women anymore or that it’s uncool or whatever. That’s not the object. Men will keep on marrying women and women will keep on marrying men at the same rate before and after (assuming they marry at all, but that’s a completely separate issue).