Concise, party of one?

It's an argument I have made on several occasions -- but never with more brevity than this:

"A frequently overheard slippery slope is:

Gay marriage = Less procreation = Human extinction.

But this slippery slope only works if we all become gay.

What process originating in gay marriage will make me divorce my wife and marry a man?

What process originating in gay marriage will make any appreciable number of straight people turn gay?"

From a commenter on the blog, Volokh Conspiracy.