>this is the part I take issue with: I don't think it *has* to be a faulty assumption
Conceptually, it doesn't "have to be" from some law of the universe, although Pareto would disagree with that, but it does in practice. Systems which leverage rather than suppress innate human desires and motivations flourish because they're not fighting nature.
>obesity is misfiring self-preservation instincts that are hopelessly out of touch with the environment
Sure, and we can see the benefit of it since scarcity has been a problem for the majority of human history. I will argue that processed junkfood should go rather than assume our biology is broken. The metaphor extends to the OP.
>sounds like zero-sum thinking to me. See it's a useful little tool ;)
It is because it's reality. I'm all for conquering the stars and getting resources elsewhere, but I'm not going to assume that will just happen automatically nor that we can continue on our current path and get there.