[pwinnski]

That is exactly the sort of assumption that caused Ehrlich to miss the target in The Population Bomb: there turned out not to be a finite amount of food. Or, if the amount is finite, we were "currently" (at the time) producing a tiny subset, as evidence by the vastly-higher quantity of food we're producing now.

As a fellow response comment illustrates, the arrogance of believing you know the "optimal number of humans" means missing out on the amazing and wonderful things future humans are going to make possible.