A thought while driving.
I've long loved the science fiction / futurist dream of establishing extraterrestrial colonies. But I've realized why it won't happen any time in the next century or so.
A colony requires a technology of production that will (in combination with trade) allow self-sufficiency and growth.
If we look at past successful colonizations, we can spot the technologies. Europeans brought technologies for dominance and agriculture, and were able to adapt technologies of the native peoples. Polynesians brought marine and agricultural technologies.
Now, some polyannas might claim we have the technologies for the Moon or Mars, and start listing solar power and other Heinlein/Clarke stuff, but it's obvious to me that's wrong. Yes we have those technologies, but they are not right or sufficient. We have a very simple demonstration why, right at our doorsteps.
It would be far easier to colonize Antartica than anywhere in space, and yet we haven't in roughly 100 years. We have some stations there, but NOTHING IS BEING PRODUCED for local consumption or for trade. (Yes, you could argue that scientific information is being produced, but face it: a real colony has a COMMERCIAL life that supports its own population.) Other excuses are easily made (for example international treaties), but if there was commercial opportunity due to technology in Antartica, we'd exploit it as fast as we exploited offshore oil: the treaties would change.
We haven't even colonized tropical shallow waters, let alone under water. Offshore oil fields are not colonized. Vast commercial opportunities await in those locations, but no colonies. Because it isn't enough to have a technology for commercial exploitation only: you must have an array of technologies for daily living of a community before you really have a colony. Otherwise you're just an outpost. It can be argued that Chilean's have a permanently occupied Antartic colony, and that satisfies the daily living technology requirement. But I'd point out that it is not a commercial success: it is a highly subsidized investment in geopolitical claims staking.