I see it from a mechanical/biological point. Boiled down, it's how much of a quasi-monoculture of humans can this planet sustain at various levels of mutual comfort. If we were in the low-mid hundreds of myriads, no problem: have all the tantalium you want - or buffalo, or whatever you can realistically find. Just a matter of price. Oops. Be it the economy or just a kind of behavioral physics, we end up doing hat many other animals - or plants - do when left alone in a place where they "just can": multiply and grow in shapes that often are exponential up to a ceiling, much like an S of sorts. But I digress. There are S-curves that spin more pleasant thought, and this gentlemen.