Earlier quoted context omitted.
The growing population of economically non-productive people requires a growing population of economically productive people to support them. At some point, you could take 100% of the output of the productive people and it would still not be enough to support retirees et al. At the limit, not growing the productive population puts younger generations in a position of existing solely for the purpose of serving the non…
But infinite population growth is unsustainable so it had to come to an equilibrium eventually. Maybe we overshot the maximum comfortable population by a bit and we are going to rebound for awhile. Also an economy that requires an infinitely growing population feels like a pyramid scheme which is also an unsustainable system.
Or not. It could be oscillatory and humanity could cyclically reverse-decimate itself while the descendants of the survivors get to enjoy millennia of the fun part of the pyramid scheme.
The big losers are whoever is part of the "perish in a holocaust" generations, and probably the first couple bootstrapper generations afterwards.