My discussion with one of our PhD students last week was centered on his concern that an asteroid collision with earth could render our planet uninhabitable.

My point was that, if we can create a livable self-sustaining habitat on Mars, then we can do the same for any currently- or eventually-uninhabitable places on earth, including under the oceans. Or, we could simply create our own micro-planets revolving around the sun, or roving spaceships.

I don't see a need to terraform Mars just to save humanity from an earthly catastrophe. With that said, if private enterprise can get it done (meaning, real customers are willing to voluntarily foot the bill), I am 100% in support of that.