>>23419977
>Can't we just colonize a planet?
Good luck finding a planet that
- has a gravity comfortable for human
- has a biosphere compatible with human

If you think about terraforming, let me tell you that it's not just costly, it's costly beyond your wildest expectation and every Sci-Fi movie typically handwave that so they can film their movie in Earth's wilderness.
Think Mars is close enough if we accept the 0.3G?
Nope, it's not, for the cost needed to terraform it you could build BILLIONS of gundam-sized O'neill space colonies. That's how massive the atmosphere it lacks is, also counting the water you have to import.

In a way, you could build giant bio-domes on the surface or the underground of a planet. Much cheaper than trying to make the whole planet like that.
But you'll be stuck with the same type of gravity and it wouldn't make resources that much accessible.
If you have the means to transport material to another planet and turn any mineral into every compound you need, then it's no effort at all to get those resources from asteroids.