I don't disagree, the OP was asking about preservering modern society.

The issue I was trying to highlight, it's not just people it's young productive people. China, Japan, Korea they are ALREADY in a population crisis. Of having aging demographics of non-productive seniors who require resources (and care etc). The US has a deficit too, it's just masked by immigration. The last number I read was that China needs 10 Million Imigrants a year under the age 40 just to keep it's current growth, but it has never had inflow immigration and they will run out of rural under developed areas to tap.

So I don't think seeing the world population decrease is itself a bad thing, but we really don't have an economic framework or model on what to do when we end up with upside-down demographics of more and more resources needed for elder care and fewer and fewer used to sustain let alone grow the economy. In a more egalitarian system maybe all this automation would help us hit a partial post-work society. In our current capital accumulation society, the billionaires will continue to own more even as the pie starts to shrink. The two easiest knobs to turn will be to raise the retirement age, lower the work start age or if you are grim-dark... let old people die or live in poverty.

And if 3rd world dictators have taught us anything, they won't care what size the pie is or how people feel as long as they (and the billionaires) continue to get to own 95% of it because they'll still be flying private jets, owning large yatchs and having parties at the French palace everyday.