Humans are in space: 3. To work 2. To live 1. To survive
The idea is that we should be out there exploring and colonizing because people are better than robots at doing a lot of things, because more life is better than less and so we should “establish habitats beyond Earth,” and because life on earth is increasingly under threat and so “If we were [living] throughout the solar system, at multiple locations, a disaster at one location would not end everything.”
These all seem like pretty weak reasons to me. People are indeed better than robots at fixing things, but the amount of work you have to do to support humans in space is enormous, which is why robotic, remotely-controlled craft have taught us vastly more about the solar system (and beyond) than any human-piloted missions. The second argument draws on a famous quotation from Frank Ramsey about the relative importance of the cosmos and humanity:
I don’t feel the least humble before the vastness of the heavens. The stars may be large, but they cannot think or love; and these are qualities which impress me far more than size does … My picture of the world is drawn in perspective, and not like a model drawn to scale. The foreground is occupied by human beings, and the stars are all as small as threepenny bits.
I like this sentiment, but it’s an odd thing to quote in support of striking out to explore the stars. Ramsey goes on to say (in his next sentence), that “I don’t really believe in astronomy, except as a complicated description of part of the course of human and possibly animal sensation.” He’s saying never mind about the vastness of the universe and our insignificance in comparison to it, focus on what’s important—other people and their thoughts and loves here, now.
The last argument is the weakest of all, but the most commonly made. Technophiles are forever claiming that the exhaustion of natural resources will eventually compel us to leave the planet or be doomed. These are also often the same people simultaneously resistant to scientific efforts to assess the scale of human-made ecological problems and optimistic about the likelihood of human ingenuity solving those problems in the nick of time. But it seems to me that if we are clever enough to figure out how to colonize space in non-trivial numbers, we are also going to be clever enough to figure out how to survive here on Earth pretty much indefinitely. Conversely, if we aren’t able to survive on Earth—given how nicely-adapted we are for living here, and with all this food and water and air conveniently provided for us, etc—we’re not going to be able to manage on Mars or Venus or Viltvodle VI, either.