You could assume the pessimistic vision in which we never start "living peacefully and within its means" (and barring large-scale changes in our biological makeup and/or totalitarian governments you can't imagine, it seems likely simply from game-theoretical considerations). But even in that pessimistic vision, we should colonize space. Why? Because in that vision, we're going to shit our bed anyway, and there's a whole universe of wooden planks and feathers waiting to be turned into more beds.

Seriously, it's not like there's some intrinsic worth in all these rocks spinning around fusion reactors. To the best that we can tell, there aren't any other sapient beings around who could claim we're infringing on their sense of beauty. It's just us, the only ones possessing the spark of giving meaning to things, and a lot of dead rocks waiting to be used.

Personally, I don't think we'll stop fighting and doing stupid things, but I feel it's entirely possible that - assuming we survive the next few decades as a technological civilization - we will fix up this planet. And space habitation could be very helpful in this in multiple ways - beamed energy, geoengineering, moving some kinds of manufacturing to orbit, experience in managing ecosystems gained on running closed-loop habitats, etc.