From Christian Davenport:

As I stated above, Mars is a HUGE challenge. And Elon has acknowledged that. It's going to be extremely dangerous. As someone once told me, say you get to Mars and the mission went perfectly. You survive the entry, descent and landing and touch down softly and everything went exactly according to plan. Even then you'd be in almost constant state of emergency given how dangerous the place is. That said, people died crossing the oceans for the first time. There is a certain amount of sacrifice that goes into exploration. But in the long run, it'd be worth it to have humans on Mars. Imagines the discoveries they'd make! And as Garrett noted above, it does have a reasonable gravity and resources that could sustain a colony. Elon does enjoy a challenge and SpaceX has pulled off feats no one thought was possible.