A thermonuclear war and the ensuing nuclear winter would shift the situation quite a bit. Which is not that far-fetched, we have the capability and have been dangerously close a couple of times. Earth might still have stronger fundamentals, but it is good to have options. And, perhaps more importantly, technology developed in pursuit of becoming a multi-planetary species might very well help here on earth too - both in our current development path and in case of disaster.

I generally agree (and I'd add: magnetic field, more sunlight - not just for temperature, but also power generation), but come on, Mars does have gravity :).

Its not that Mars would be better or even equal, but that it would be a second chance, just in case.

We're all going to die. And if we don't get killed by something else, we die of cancer, eventually. Death, taxes and cancer are as close to a trinity of certainty as you can get, and I'm not sanguine about finding a "cure" for conditions that represent the terminus of a lifetime of wear and tear on the body, at least on actionable timescales.