Elon Musk, the billionaire founder and CEO of the private spaceflight company SpaceX, wants to help establish a Mars colony of up to 80,000 people by ferrying explorers to the Red Planet for perhaps $500,000 a trip.
(...) we've put all our eggs in one basket. If we were on many worlds and were to mess up down here, there's a way for the human species to continue. I don't for a moment propose that the Earth is a disposable planet, and we have to put enormous efforts into making sure we don't muss up down here. But there is a chance.
I am a fan of the idea since they announced it and I wouldn't see why someone on here could be against it.
We have no idea if a self sustaining colony is at all feasible. If it cannot eb self sustaining than it doesn't reduce existential risk at all and (as well as opportunity costs mentioned by others) distracts attention and political capital from keeping earth habitable.