I don’t know how many people we should have, but there are some metrics we could look at and maybe say beyond a certain point managing these metrics becomes harder as we scale, or even impossible.
If we had kept our population low enough, we could have subsisted on a timber and whale blubber energy policy indefinitely. :P
edit: It’s always a controversial opinion to say there are too many people, but there probably are, at least the way we are behaving in this world. Many of the problems we are fighting are symptoms of us trying to scale upwards as hard as we can so we can collectively use our credit cards and hand the debt off to multiple kids. It’s a bad practice.
edit: TIMBER and whale blubber energy policy, fixed typo