Earlier quoted context omitted.
We’ve already reversed population growth everywhere except Africa and they’ll only be a decade or two behind. We need to stabilize it if we’re going to avoid population and then civilization collapse. Civilizational collapse is bad for the environment btw since it will mean a return to burning coal and wood and the removal of all environmental regulations on pollution and exploitation.
You're speaking in certainty when there's no actual direct link between a reduced population and needing to remove environmental regulations. They seem fairly orthogonal. Sure an argument could be made that it could happen, but that's not how you're presenting it.
Doing all of that while the available labour, researchers, economic output and tax base shrink is a dangerous minefield to walk through. It may result in a feedback loop that crashes everything.
One of the scariest things to consider is if we are replacing 2 people in a position with 1 person then that single person now needs to learn the tacit knowledge and technical skill of 2 people they are replacing. That’s a recipe for lost knowledge and regression if I ever saw one.