I definitely agree in principle, but on the other hand, it's really hard to imagine an event that would render Earth less hospitable than Mars. In general, these catastrophes would just make Earth more like Mars.
Nuclear war? Mars is a desolate wasteland that's bombarded with ionizing radiation from space (because it lacks both a sufficient atmosphere and a magnetic field to protect it).
Asteroid impact? Unless it eliminates all of our atmospheric oxygen, ozone, hydrogen and nitrogen and drops the average surface temperature to -55°C, we're still better off here.
Pandemic? If we can protect a colony from the environment of Mars, we should be able to keep at least that many people safe from a pandemic. (Just stick your Mars-bubble in Antarctica if nothing else. It's a lot like Mars except it has better temperatures, an atmosphere that you can breathe if you need to and the water is more readily available.)
All of that's true in the short term, but if we do end up getting millions of people sustainably living on Mars, these specific catastrophes would be less devastating to the human race as a whole.
I have to say that motivating with fear puts red flags up in my mind as I'm sure it does with the rest of the crowd here. If I were a politician, I'd see the mission to colonize space as an effective way to unite the world behind a single goal. Since I'm not, I have a different view which is that AI has the greatest potential to solve humanity's problems. But that's another discussion.
You could replace 98% of the earths atmosphere with Methane and it would still be more habitable than Mars. (The only way methane would make it worse is if you turned the atmosphere into a fuel air bomb and a few weeks after the detonation it would one again be more habitable.)
Well, I was referring to the hypothesis that the release of previously sequestered methane caused the Permian-Triassic mass extinction event where 96% of marine species and 70% of land species died [1]. I think it's fair to say that a poisonous atmosphere is less habitable than no atmosphere.
Exposure to the Martian environment would kill 100% of species that we know of. If that has happened on earth before, we can say pretty definitively that elevated levels of methane are less harmful.
Earth's is 101,000 Pa dropping to 30,000 on top of mount Everest. Mars's mean surface pressure is around 600 pascals which is below waters triple point which prevents water from forming regardless of temperature. http://en.wikipedia.org/wiki/Triple_point Still that's close and in some creators the pressure increases high enough so it's possible for water to form.
Unfortunately, on top of that what makes the atmosphere truly deadly is a lack of Nitrogen one of the primary building blocks for organic chemistry.
Nuclear war? Mars is a desolate wasteland that's bombarded with ionizing radiation from space (because it lacks both a sufficient atmosphere and a magnetic field to protect it).
Asteroid impact? Unless it eliminates all of our atmospheric oxygen, ozone, hydrogen and nitrogen and drops the average surface temperature to -55°C, we're still better off here.
Pandemic? If we can protect a colony from the environment of Mars, we should be able to keep at least that many people safe from a pandemic. (Just stick your Mars-bubble in Antarctica if nothing else. It's a lot like Mars except it has better temperatures, an atmosphere that you can breathe if you need to and the water is more readily available.)