[plenipotentiary]

"rising productivity more than compensates population declines as we can run the country with fewer people" and "we have more spare resources for people, hence a higher quality of life"

Agreed.

For people who advocate perpetually increased population, I would ask what will they say when the whole planet has standing room only only, and the next child has to stand on someones shoulders?

[B4Ranch]

I don't see the problem as only being one of perpetually increasing population but from one of longer lifespans also. 100 years ago when one got sick they either died in much shorter timespans than we see today or became healthy again.

[NeoCaveman]

For people who advocate perpetually increased population, I would ask what will they say when the whole planet has standing room only only, and the next child has to stand on someones shoulders?

By the time we get to standing room only, we'll start colonizing the moon because we need the space. Necessity is the mother of invention.

Imagine how much ingenuity you lose with a shrinking population.