But. Really. What's the threat model here?
Mars is meant to be a backup of humanity. OK. Against what threat? We can think of many, but a self-isolating base in the Antarctic would survive nearly all of them with better conditions than a Mars base.
Nuclear armageddon? Not much fallout over Antarctica and OK, you can't go outside of a while. Still better than Mars where you can't go outside ever.
Runaway global warming? The ice will melt but at a slow pace that leaves plenty of time for adaptation, the climate will become more hospitable at the poles rather than less, and at least you will have lots of fresh water. Unlike, say, on Mars.
Global pandemic? An Antarctic base can self isolate, no problem. Just lock the doors and let anyone who tries to reach you freeze to death. A serious Mars base would need some sort of border control policy too, if Musk had made it cheap to get there.
Massive asteroid strike? I guess it'd wreck the atmosphere but ... well, then you're no worse off than on Mars which doesn't have one to begin with. And you're much more likely to get nuked by a 'roid on Mars where there's no atmosphere to burn it up.
I dunno man. I'm trying to think of a problem that a serious Antarctic city couldn't solve and coming up blank. Short of Earth getting sucked into a black hole or something, what scenario is survivable on Mars that isn't at the poles?
