@Justhuman14 what i really dislike about that response to gay marriage is that it implies that just because a few gay people want to get married, everyone will become gay. Believe it or not, most of the population is straight, so jumping to that conclusion is pretty out there isn't it?
But let's say you were right. Gay marriage is legalised and everyone instanteously becomes gay. Where will all the babies come from? Adpotion will only work in the short run, and so will sperm banks. But it's actually pretty simple.
Say you have two couples living next door to each other. One gay and one lesbian couple. Both of them would like children. Now obviously, having sex with each other would be out of the question. But to say that in 100 years time humankind would be too dumb to know what to do when we have loads of women with eggs and no sperm and loads of men with sperms but no eggs, you obviously have no hope for us as a species.
now back to the real world where only about 4% of the population is gay. You have nothing to worry about. Arguing against something by stating what could probably maybe happen if it were taken to the extreme (which is pretty much impossible in this case) isn't a valid reason