I'm not saying we shouldn't try to colonize Mars eventually, but keep in mind that even after a nuclear war, major asteroid impact, pandemic, runaway global warming, or almost any other catastrophe we can dream up, Earth would still be more habitable than Mars is.
Absent the Sun going Nova or something knocking us out of orbit somehow, there will be some parts of Earth that are still safe. Even if we end up needing to build some kind of underground sealed habitat to live on Earth, we still won't need to compensate for as many things as we would to build equivalent-size habitats on Mars. And we'll already have an enormous industrial infrastructure in place to do it with, and we won't have to ship things across 2 gravity wells and a 9-month space journey.
True, absent the consideration of enclosed habitats on Mars that are self sufficient. But I see your point, it's easier to survive on Earth in many such scenarios, perhaps even unaided by tech, and on Mars you absolutely need to rely on tech.
But still, the existence of such a colony on Mars would be valuable. Civilization gets another shot, in this hypothetical case.
Absent the Sun going Nova or something knocking us out of orbit somehow, there will be some parts of Earth that are still safe. Even if we end up needing to build some kind of underground sealed habitat to live on Earth, we still won't need to compensate for as many things as we would to build equivalent-size habitats on Mars. And we'll already have an enormous industrial infrastructure in place to do it with, and we won't have to ship things across 2 gravity wells and a 9-month space journey.