Such a loaded topic, I know. It's difficult to separate personal convictions from public policy from hard science, since all are inevitably intertwined. Instead of advocating a heavy-handed dictum for how everyone "should" act, I'll instead loosely brainstorm seemingly disparate themes. And so on.
Every environment has a carrying capacity, which is the hard limit that particular space can support life. This is not a dispute. Just as rats in a cage will breed to the limit of their space, food, and water, so too does any organism on the planet. For the large majority of Earth's history, species have been limited to their environments based on their physiology. That is, if a bird had a beak that could break the shell on a specific type of nut, then they could thrive by eating it. This is called adaptation.
Up until humans that is. We bent the rules. We have these brains that let us alter ourselves and our environments faster than evolution would normally allow. Instead of waiting a million years for someone to mutate with a claw that can crack a walnut, some smartypants came up with a nutcracker. Instead of scavenging the land for berries, somebody had the bright idea that if we planted all the berries in one place they could pick them a lot faster.
Humans have the evolutionary ability to increase our carrying capacity. It doesn't mean we don't have one, it just means that every good idea some brainiac comes up with increases this number.
The inverse is also true. Without the technologies that we currently possess, the carrying capacity of humans would plummet. Without nutcrackers and modern agriculture, billions of people would find themselves starving to death.
At this point, I want to take something from religion, without getting too dogmatic. This idea is the Four Horsemen of the Apocalypse. I'd like to discuss the Famine, War, Pestilence, and Death version. (The older version, in my opinion, was before they had a group consciousness about disease.)
The Four Horsemen seem an awful lot like personified regulating factors. (Just as God and Devil look an awful lot like personified Good and Evil.) That is, whenever humans start overpopulating, people starve, fight wars, get sick, or just plain die in all of the usual random ways. This idea is not new.
There is also the mistaken idea that we can somehow push back these factors forever, and that one day the carrying capacity of humans will be infinite. This ignores a fundamental fact: our ability to adapt is not perfect. There is a certain amount of compromise involved. Every technology we put forth has detriments, as technologies like the internal combustion engine, intensive farming, and nuclear power have shown.
Now it would be easy to say at this point, "Well, let's all just stop overpopulating. Let's use contraception." However, a disturbing popular culture reference to this idea is the movie Idiocracy, in which "smart" people stop breeding, and are overrun by "stupid" people. Or take a government imposed restriction on population like China, where the one-child policy leads to many ethical dilemmas. Even something as gentle as a one point difference in fertility rate has a huge effect on social policy. Check out the U.S. and Mexico on this map. It's no wonder why immigration reform is such a huge fiasco.
The elephant in the room is the uncomfortable idea that any group that applies self-regulation to their breeding will be replaced by those that don't. Which is why I refrain from cheerleading a solution when all of the options are distasteful, some more than others. This is a choice between many evils: allow the Four Horsemen to collapse wayward societies or implement immoral social policies? Do governments have the authority to make this decision? Do people have the rational self-interest needed to regulate their own urges? What about those that don't? Do we have the right to implement limits for "their own good?"
I fear any wellmeaning attempt that leads to a hellish dystopia, while at the same time I foresee a societal collapse on the horizon. Which is why this topic is bigger than any one person, me included.