• Small colonies are impossible wherever they go, small groups are intriniscally non-viable. Expansion is impossible away from Earth.

  • It's cheaper to UNDO damage we've done, with unspecified technologies that do NOT exist, change all existing cultures, and it is safer to meddle further with an ecosystem we don't know how to manage now, than to plant seeds elsewhere. This is more viable than to improve existing technologies to go to places out of reach of the coming disaster as a backup. Above all, the attempt should be avoided.

  • A rocket adds so much more (on a global scale) damage to the ecosphere that extra-terrestrial (planetary/lunar) colonies would doom us all. Well, more doomed.

  • Humans having their own agenda is a bad thing. Central planning and control is all - their agenda would certainly have not include survival (the goal involved here).

  • Humanity would be better off with a nomadic/tribal lifestyle - after all it is idyllic and wouldn't have the problems you cite for colonies.