“Necessary”, no. We’re all fine here on Earth, where we evolved, and all that. We’ve gotten along just fine without leaving the planet.

Desirable? Yes. But, I think we should do it with robots, because humans are too expensive due to being so fragile. Also, what should we do with what we find? Exploiting the resources of the Moon and Mars should not be allowed. Setting up human colonies there seems extravagant at this time.