How does permitting people who are homosexual to express their relationship publicly in any way prevent men and women from fucking each other?
A prominent husband-wife historian team once wrote of the lessons of history: "Sex is a river of fire that must be banked and cooled by a hundred constraints if it is not to consume in chaos both the individual and the group."
Our society has set itself for full-scale consumption. We have donned the gasoline-drenched firecracker suit and are currently descending into the lava. I honestly do not believe we will make it more than 1 or 2 more generations without complete social collapse, and I think acceptance of homosexuality and furthermore government endorsement and reward of homosexuality via grant of marriage are tokens of this extremely broken social consciousness. If you look back through the 20th century you can trace the disintegration step by step, and now we're just a smidgen short of ripe. I fully anticipate that ripening to occur, and modern Western society to drop off the tree and into the flames.
Our economic house of cards will be crashing down within ten years. You should probably worry about that first.
Besides, over- or under-population being a problem is related to the economy too. It's all about having enough resources and jobs for everyone, right? The best possible thing any government can do for an economy is to keep its hands off of it and let people produce and accumulate wealth.
Then there's the US police state, which probably won't take long to complete. That's another much more pressing concern than whatever might happen with regard to the population.
Seriously, what is your thesis here? What do you think is happening? "Oh honey, I just saw two gay men in the park. Let's never have children." ?
Perhaps we should shut down our education systems, health systems and welfare, and tax anyone outside the "1 percent" into poverty in the name of procreation.
(just in case, this being the internet and all: that's sarcasm)