We could support more population if we lived sustainably. We don't. Humanity came through the Toba bottleneck 70,000 years ago. We are better off if having a population collapse-- so biosphere can recover. As to our approx. 8 billion, it's too many and we aren't adjusting to sustainability quickly enough. There will always be some who are fertile, given our vast numbers, so fears of extinction of sapiens (by this) are overblown.

This is a boon for the birds, bees and world.