Re: @DanceMan
"That most certainly was not implied. Humans have existed (briefly) on the moon, and that didn't help with population pressure on the Earth in the slightest."
That's exactly what is implied.
That the Earth is the only place that support any reasonable size of population and the only energy sources are those that can be found on planet Earth.
The energy cost to LEO is about the same as the round trip energy cost of London to Sydney (a fact known by Philip Bono since the late 1960s). An LH2/LO2 system would deposit most of its exhaust back into the atmosphere for recycling. So yes mass migration even using rather pedestrian means (no space elevators or tethers) is possible.
As for the Earths energy consumption the Earth covers a disk of roughly 127 million square kilometres. That is roughly 1/2.19x 10^9 of the sphere around the Sun at 1 AU.
Assuming the current Earths energy consumption is about 150 peta watt hours That a sphere at the Earths radius at 10% efficiency would collect 50x more energy than the entire worlds energy consumption.
The issue is not wheather those resources exist, because they do. The question is can be find a way to exploit them economically?