Somehow this sounds a little bit more expensive than just using existing arable land or existing potable water
Of course. My post was meant for people, who'd claim, that "Earth can not sustain" such a big population — by listing the vast areas, where the new billions could live in comfort even if those existing parcels of arable land and sources of potable water were exhausted.
I refer you to Project Orion
The method could allow us to reach other star systems, but not practically — not within reasonable time. For that, we'd need faster-than-light travel and that is, what I had in mind.
Because that [ping times -mi] is the main downside of the Malthusian catastrophe.
It was a joke, relax...