> which is the very definition of a pyramid scheme
AFAIU, population growth being beneficial is predicated on the notion that not only does every additional human contribute a pro rata factor of N=(contribution/cost) wealth to society, where N is greater than 1, but more importantly that for every additional human N increases.
Maybe some professional economists can cite to the particular theories and research (I'm too distant from my academic days), or alternatively disabuse me of this notion. But that's my understanding, and in that light population growth is definitely not a pyramid scheme.
It doesn't mean that population growth is the only way to increase N. There may be ways to increase N fast enough to compensate for the loss of the population growth dynamic, but those ways seem to be fairly elusive.[1] It also doesn't mean that there aren't pyramid scheme-like dynamics elsewhere (e.g. land use, housing prices, etc); they're just not intrinsic to the overarching dynamic.
[1] And that's because rate of innovation is partly a function of population size. The more people there are, the more risk takers exist, the more opportunities available, the more possible social arrangements, etc.
An analogy: To a first approximation, the more neurons you have (population), and the more interconnected they are ("free market"), the more capable and potentially intelligent the network.