[PeterisP]

If a "evaporate a big city" or "kill all humans on Earth" asteroid strikes, the existence of a Mars colony doesn't help my personal survival or well-being in any way whatsoever unless I'm there.

And if I'm there, odds are that it made my personal survival chances worse, since they're mostly determined by the many "normal" causes of death and being a pioneer in a world not really suited for humans is likely to be worse than Earth.

You could make an argument that it's not wise to put all your eggs in one basket, and it has some merit in this discussion, but when all I have is one egg, the only thing I can do is to pick the safest basket I have - and for now it's Earth.