[ef4]

The biggest barrier to doing interesting industrial stuff in space is the energies required.

But the whole context of this discussion is a society that has thousands of times more energy available than we do today. That's why it's not at all unreasonable to include space in the discussion. It's hardly fair to posit advanced technology that decreases the cost of energy by a factor of a many thousands while claiming that dropping the cost of space transport by a mere factor of 100 is unreasonable.

No new physics is required. We already know how to build lasers that could lift cargo into orbit -- it's just a question of energy cost.

Habitability is irrelevant: space is for robots. We already know that population growth will level off in only a few decades, so "more people" is not the problem -- it's "more industry". The industry doesn't need to be where the people are -- not when our robots are already good and getting better very fast.