If we can't keep the planet to which we've spent a billion years adapting habitable, if we can't protect areas of it from outside influences, we can't do it anywhere else.

This whole notion of "after we've wrecked and sucked our home planet dry, we then need to move to colonize other worlds" really sucks, and is actually pretty depressing isn't it.

Also, that silly nonsense about "our sun will blow up in 6 billion years time so we'd better start colonizing other solar systems asap" must be one of the most idiotic and in fact, dishonest forms of motivation for anything that I've ever heard. We don't know how we'll survive this century - let alone the next 6 million centuries.

Bottom line is, the true and best motivation for manned space travel is about exploration for its own sake, and also as Hank said, a certiain kind of spirituality, which we'll never get from machines alone. - And about new experiences, standing under new suns and constellations - expanding human consciousness in physical reality, not just in meditative navel gazing.