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.
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.