Mars does absolutely nothing to ensure the survival of the human race. At best, you're condemning a bunch of colonists to a terrible death if something happens to mothership Earth. (or, much more likely, some petty squabble on Earth leaves the colonists to fend for themselves)

I know Elon said it all those years ago and then everyone else jumped on the bandwagon. But, it's a quite facile take on the issue that's more about wish fulfillment than reality.