The Antarctica idea is a good illustration of the most important thing about Mars: it's _over there_. If you try to settle Antarctica, you will quickly discover that there are lots of international agreements about who is allowed to do what, and you will run afoul of one government or another pretty quickly. Mars is both too far away to be easily messed with, but just as importantly too far away for governments to really care about. They are unlikely to bother sending a nuke to Mars because it's way over there. Antarctica, if it became a place of any significant population at all, would have much more geostrategic significance, I think (not as much as the Arctic, but still a lot).