It's got nothing to do with overpopulation, or mining or technology.

The point of space travel is for adventure, for the challenge, because it's new and interesting and not many people have done it before.

Part of what makes it so attractive is that it's so difficult. Who cares if we can establish colonies there or not – people want to explore and find things out for the sake of knowing the unkown and acheiving things that have never been done before. It's like the Olympics – what is inherently useful about running 100m in under 10 seconds? Nothing. But it inspires people because it challenges them to achieve things noone else has – exactly the reason so much money and effort goes into travelling into space.