I'm not claiming that life on Mars would ever be easier than life on Earth. But there are plenty of ways in which nasty things could happen on Earth that the po

I'm not claiming that life on Mars would ever be easier than life on Earth. But there are plenty of ways in which nasty things could happen on Earth that the population here is simply not prepared for. A major asteroid impact or supervolcano eruption could cause terrible weather for years (even if we don't go all the way to the "atmosphere is a pizza oven" point), and it would be awfully tough to keep feeding our cities. At that point, most industry collapses, and we're all interdependent enough that the ripple effects could wipe out the vast majority of the human population, or even all of it. Having a self-sufficient population on (say) Mars would make it likely that some portion of human civilization would survive such a disaster. I guess you might argue that we could achieve much of the same effect by using the same technologies to establish self-sufficient populations in safe(r) locations right here on Earth: underground or deep underwater, for example. But those would still be more affected by local disasters than a colony off-planet would be, and I feel like it would be harder to recruit people to live there (and harder to guarantee that they were truly self-sufficient). As you say, Mars would attract the adventurous. The Underground Civilization Vault would just attract the astoundingly paranoid.