We do not need more people on this planet. It will only increase the likelihood of a major catastrophe like famine -> war -> nuclear war, which will then put scientific research back decades if not centuries.
From which growth-based economies will those rewards be taken? If not that way, then how?
The whole point is that I am assuming there isn't enough incentive on a large scale to deal with environment problem BEFORE they occur. With global warming, once we go past the point of no return, it won't be a quick fix. We will throw the equilibrium out of whack. If we were to pragmatically balance things now/going back a few decades, we could avoid the big swing that will occur.
So basically, the population may fall from 8 billion to 3 billion because of famine/war, etc. Immensely painful things... Or we could just have pragmatic restraint through rewarding sustainability, and it would naturally level out to 5/6 billion or whatever that number is... but without the immense pain of billion fighting/dying.
I could not be more diametrically opposed to your position. It's clear to me we have far too many people as it is, and the only way out is through population decline. Anything else is ridiculous line noise to argue about. Once you solve the CO2 climate change problem you have about 10 other just-as-bad crises right behind it if population growth continues.
Sure, as you say there could be some more black swan events in science/technology that technically lets us expand in the short term much like modern agriculture has. I don't see that as a positive as it simply delays the inevitable and makes it even more impossible to recover from.
There is no choice but to grow. People like to travel, conduct scientific research, and face and conquer new technical challenges. You cannot do this without more people and the productivity they provide. Period.
There are enough people in the US now, enough children, that our education system could focus better on technological and scientific advances for those who show the aptitude (by increasing opportunity and decreasing inequal access to education and jobs).
At the same time, prosperous cities are booming and rents are rising. It's polarizing.