We'd be much better off building colonies on the bottom of the ocean than on the moon or mars (or a cylinder floating at a lagrange point.) After we run out of

We'd be much better off building colonies on the bottom of the ocean than on the moon or mars (or a cylinder floating at a lagrange point.) After we run out of space on the ocean I suppose it will make sense to consider space colonies, but I think you are really underestimating the technical challenges.