We certainly can't have a stable society with a rapidly shrinking population.
You need to know what the current population is, what the carrying capacity is, etc etc.
Generic statements sound and feel good, but are completely useless.
This is just the natural and obvious outcome of what we’re already dealing with. The fertility crisis is just our refusal to deal appropriately with the ultra rich and the collapse of our institutions.
Yet we have made (hopefully this is not contentious) great strides in technology, human rights, and general quality of life.
Certainly there were some stable societies in that timeframe?