If we can't even save our own home world, there is every reason to believe that we will do damage elsewhere. That being the case, best to stay home until we grow up a bit.

Earth doesn't need saving, it's perfectly fine. Regardless, in a world with practical interstellar travel local damage is irrelevant - the universe is infinite. Milky Way alone contains at least 100 billion planets.

I rather suspect fossil fuel usage, deforestation, etc. won't be an issue on Mars.

That's great; but Mars, and even the solar system, is not "the universe".

I suspect we're likely to solve greenhouse gas emissions long before we're able to get humans out of the solar system.

The one easy option, voluntary restraint, isn't even on the table, not that I noticed. So what makes you think that's so likely, what about our current priorities and behaviours makes you so optimistic? Where is the economic incentive to solve the problem? Sure, it means more long-term life and profit, but having even 1% less quarterly profit so that in 1000 years some other company can exist at all is not exactly how we do things around here. Instead companies invested in fossil fuels are happily funding "global warming skeptics".

That proverbial man who plants trees knowing he will never sit in their shade is proverbial for a reason.. it's an amazing and heartwarming little saying because it's a contrast to how we generally behave, as individuals as well as organizations and masses. We learn from repeated catastrophe.. sometimes, maybe. But this problem is not one we can have a lot of attempts at solving. Right now we are still moving into the wrong direction, and probably even accelerating.. sure, hitting a wall can make people change their direction, but not if it breaks their neck, so to speak.

> So what makes you think that's so likely, what about our current priorities and behaviours makes you so optimistic?

I'm not enormously optimistic. I'm just saying that compared to interstellar travel, avoiding fossil fuels seems like a fairly small problem.

I suspect that in turn depends on whether we're able to create 'digital' humans or not.(I'm not weighing in on whether or not we'll be able to, just pointing out that if we can, 'manned' interstellar travel becomes much, much easier.)

The rest of our solar system is rocks. Hard to do much damage there. Anything we do has to be for the better (oxygen, water, life).

Are you sure? I get the impression we're not very good at recognizing other life forms, or alternative forms of intelligence.

So we kill them. It wouldn't be the first time, and it won't be the last. This is life. Hopefully we'll learn something, except to be paralyzed by fear of doing damage.

What is damage? Life is change. Life modifies the environment. The Earth does seem to be the most interesting body in this region of space, but I don't view it as some sacred jewel that should be protected against all change.