So increasing population seems to me to be the true problem, but who is going to be brave enough to talk about forced population reductions?
No one. Not that it would matter.
But, you’re right. The Earth is probably able to sustain a few billion more people. But it can’t sustain even its current population if they all consume like Westerners, and being able to consume like Westerners is the goal of every aspirational peasant in every developing country.