Once we get depressed and nihilistic and give up, the universe will be forever deprived of the colour and drama human civilization can add to all those bare rocks up there.
I never considered that the implication is we could live here sustainably, but you’re right.
These discussions tend to be heavy on Asimov-inspired scifi-think and weak on just taking a walk in a forest on a nice sunny day in late spring. All this talk about having to colonize space is just rubbish, compared to the wonders of nature that would be worth preserving.
But the audience here is strongly biased. If most of your day is spent in front of a computer and reading scifi novels in the evening, then that's where the discussion moves.
Also, are you saying that forests are nature and space isn’t? Or are you saying that there aren’t any wonders of nature to experience out there?
Setting up nice sunny walk-ready forests in space is something that’ll take centuries, but if we don’t do it we’re doomed. Incidentally, so are the forests.
Humans establishing self-sufficient communities beyond Earth would prove that humans have the capability to thrive sustainably on Earth. It would silence forever any technological objections to the possibility of human sustainability on Earth.
And a firm idea that humans can never establish self-sustaining communities in space is not that far from the idea that we probably cannot do so on Earth, either.
It really is not a huge step from pessimism about human future (ie in space) to nihilism about sustainability on Earth, and I do wish people would acknowledge this more: people enthusiastic about permanent settlements in space are, in fact, more certain about the possibility of sustainable thriving on Earth than the space-pessimists are.