I hear this point made often, and it always seems problematic to me, unless you're looking at a (very) long-term plan.
If we're going to put our eggs in more than one basket, the first thing we need to do is find more baskets. While the technology to create permanent human colonies in space is near at hand, the technology to create independent space colonies isn't anywhere close. If a colony doesn't have significant travel, mining, and manufacturing facilities, plus the ability to sustain itself for at least a few hundred years, and a very respectable gene pool to boot, it's not worth counting as a basket. If the earth goes down, the big metal doughnuts out there will probably be empty shortly thereafter.
Living in a sustainable way on another planet is a better plan, but it isn't going to be any easier. We're basically talking about terraforming Mars, or leaving the solar system. Anything like a moon base is going to have the same critical problem as space stations: they won't survive without an elaborate earth-based support system. Sure, the moon-men could potentially travel back and repopulate an empty earth... but if that's the plan, we'd probably be better off keeping some remote, self-sustaining colony here, and saving them the trip.
I do think there's reason for optimism about space, in part because nothing gets done without at least a modicum of optimism. For the foreseeable future, though, count me as a pro-science not-very-hippyish type who thinks taking care of things down here is the only real option for survival. We're surrounded by lots and lots of nothing, very occasionally punctuated by an extraordinarily hostile something.
By the way, I voted for "reduce the cost of putting things in space". In my opinion, the faster space technology gets out of the hands of cathedral-builders (to whom we owe a lot), and into the hands of entrepreneurs, corporations, hobbyists, hotel chains, adventurers, and crack-pots, the faster we'll start to figure out how to really get things done up there. Then (the free-market faithful say) we'll get all the other things on the list done better and more easily.