Anyhow, I thought of this issue when I ran across this passage today about spirits from Jupiter. It supports the idea that a planet can only sustain a certain number of people and talks about how the attitude of the people on the planet significantly affects how many people it can sustain.
[The spirits from Jupiter] declared that the region of the planet where they had lived was inhabited by a large multitude of people, as large as the planet could feed, and that it was fertile, producing an abundance of everything. They also declared that the inhabitants there desired nothing in excess of the necessities of life, and that this was why the multitude of people was so large. (Arcana Coelestia 8116)