What would really happen to "Quantum Fusion"

[cprise]

10. Good point about reproduction rate response

But my comment about overheating was meant to show that without Mr. Fusion we could continue with worsening global warming, and with Mr. Fusion the resulting increased consumption patterns would create a fundamental thermodynamic waste-heat problem that the extra on-hand energy could not undo.

Perhaps in the later scenario, the increasing use of energy to cool the planet would simply make Mr. Fusion's abilities look more limited and consumption would be checked. Or perhaps a limited reproduction factor as you pointed out, would leave people with just a consumption bell-curve where desire for stuff/services also becomes limited. But the top of the population or consumption bell curves could put the planet well past what the biosphere could withstand.