I don't think it's a matter of needs or wants, I think this is too big for any individual or group to deal with. The answer will be emergent. The population will get to a sustainable size because it must. I think nature will decide how it happens. Just like it does with overpopulating reindeer or rabbits. Predators, disease or famine. Free energy won't help either because energy isn't the only limiting factor. In fact it would probably make the situation a lot worse. It's the main reason I decided not to have kids.