I think Earth after nuclear holocaust or reasonably likely asteroid impact is still significantly more hospitable to human life than Mars. And any gamma ray bur

I think Earth after nuclear holocaust or reasonably likely asteroid impact is still significantly more hospitable to human life than Mars. And any gamma ray burst affecting Earth would hit Mars too. Building survival silos on Earth would be cheaper and likely more effective to save the species in these situations. Elon often talks about how exploration is exciting and inspirational and a prerequisite for future interstellar travel, and that works better as a justification to go to Mars, IMO. Also, while those disasters might not completely wipe out humans on Earth, they could reverse centuries or millennia of progress and delay further space exploration for hundreds or thousands of years if we don't do it now while we have the chance.