There is a discussion that ought to precede the discussion of space colonization, but which almost never happens. Before we can decide whether or not "we" should colonize space we first need to decide who and what "we" actually are. The tacit assumption is that "we" are homo sapiens, that is, the flesh and blood phenotype of the human genome. But that might not be the best answer. Another possible answer is that "we" are our ideas, our culture, our art, our philosophy, our scientific knowledge, and that this transcends our biology. In other words, maybe what matters is the software, not the hardware. The reason this is worth considering is that it's a hell of a lot easier to send our software to other planets than our biological hardware. Our bodies have evolved to live on this planet. Sending human bodies into space is rather like putting a fish in a ziploc bag full of water in the middle of the Sahara desert and expecting it to thrive.