Population rises as a response to insecurity in living standards. The conditions we know of that promote instinctive long term population stabilization and/or reduction are all related to economic security.
As for "overheating", again that is an issue that has roots in economic scarcity. If you have unlimited free energy I'm pretty sure some method of reversing climate change is a reasonable proposition since carbon sequestration is really limited in the present world by the energy costs it requires.
What happens to "consumer" demand when you eliminate the profit motive? Since the entire concept of "consumer" is an outgrowth of capitalism I think that it's reasonable to speculate the values by which we judge what one "needs" would undergo significant change.