The world population has been over 1.5 billion for well over a hundred years and we're still here. But I agree adjustments need to be made. One problem is that countries that can afford to have kids aren't, while those that can't, are. Lot's of young people in India, lots of old people in Canada for instance.
Populations under threat ... reproduce.
Forces of nature, more children, more chances some will survive. Also more people to help out?
Not sure why, but ... people in comfortable circumstances do reproduce less.
I learned to withold water and fertilizer from some plants because they only flower under threat.
Made me think ... Lol