If Elon actually wants to go to Mars because "we can't keep our eggs in one basket", why isn't he building a huge underground shelter on Earth in the meanwhile? 99% of all the events that have a potential to actually threaten human civilization would still leave the Earth more habitable than Mars is now. And a majority of catastrophic events that would render Earth less habitable than Mars would destroy the Mars base too. So Mars base only really helps against a tiny fraction of events that render the Earth completely uninhabitable yet somehow spare Mars. Now if you do the math you will see that an autonomous underground city somewhere on Earth would cost a tiny fraction of the Mars base yet would provide like 90% of its civilizational insurance value. And it would help to develop technologies you need to live on Mars anyway. If he actually cared about the survival of the human civilization that's a complete no-brainer. So why isn't he putting a fraction of his efforts into this?