Not destroying the Earth seems pretty critical to everything. Getting the technology to travel to and live on Mars would help that goal. Think of the benefits things like generating power in space and moving heavy industry off of Earth would create.
That's highly debatable. We talk a lot about global warming, which is due to CO2, which in turn is due to fossil fuels. So of course it sounds like it is an energy problem (and generating power in space, if that was actually better in terms of CO2 emissions, could help).
But what we always forget is that the mass extinction we are living right now (i.e. "we are destroying life on Earth") is not a consequence of global warming. Remove all the CO2 from the atmosphere right now, and we are still in a mass extinction. CO2 will just add global warming to the problem, but that's only a bonus.
Agreed. But there are many examples. Take food production, which is one of the largest environment killers. Keeping people alive in space will involve novel food producing technology that might help stop people on Earth from destroying forests for grazing land, etc.
