Oh, for the love of God.
And yes, I'm aware of the irony in that statement. I don't believe in the Catholic's concept of God, or anybody else's. But I'd like to think that, if the Christian God were (or is) real, he might be a fan such things as basic logic.
Listen up, Benny: there are seven billion people on this planet. Seven. Billion. Seven zero zero zero zero zero zero zero zero zero (85% of which aren't Catholics, by the way). The things that threaten humanity itself are, in no real order; asteroid strike; nuclear war; super-charged flu pandemic; and a shadowy international conspiracy of murderous leopards.
And running out of room. The natural world can offer plenty of examples of species and local populations who plummeted to their extinction just after reaching their highest ever numbers, because they eat all the food, drink all the beer, and generally carry on with no more thought to tomorrow than Bill Murray in Groudhog Day. The human race isn't there yet, of course, but we're a damn sight closer to it than we are to being wiped out if gay people get to tie the knot. At least when your predecessor banned in-vitro fertilisation, that was a move in the right direction, cold-hearted and nonsensical though it was. 
I'd actually have more respect for the Pope if he just came out with "Dudes, it's in the Bible. Go check that shit out." That raises other questions, of course, but at least it would be honest. Trying to dress up common-or-garden homophobia as a principled attempt to save humanity is the highest form of bullshit, and it's cowardly as well.
 Perhaps this whole thing is a two-pronged attack to ensure The Forever War never comes about. I can't imagine the Catholic hierarchy getting along too well in a world where overcrowding issues have been solved by growing all new people in vats, and turning the entire population gay to prevent pregnancy. It's a neat idea, and demonstrates conclusively that being the only straight man on a planet filled with lesbians isn't nearly as brilliant an idea as Nuts might want you think.