Dreams of manned space flight

I'm in Mountain View this week, for the Mozilla Platform team work week. Matthew and I went up to the NASA Ames Research Center on Sunday, which was awesome. There were some interesting exhibits there, including a moon rock, which was protected by two layers of perspex glass. They also did a cool presentation on the Spirit/Opportunity and Phoenix Mars missions. They detailed the landing sequence and the activities of the robotic landers. They complained about how budgets where always cut, and compared the cost of manned space flight against robotic missions.

Amongst the NASA scientists, there exists two camps, one whose argument is that it's currently unnecessary and too expensive to send manned missions, the other camp believes that it's human nature to explore, therefore we should go. I used to believe that people should go, if I was offered a ticket I wouldn't hesitate, but I can't agree with the "human nature" agrument. It's also human nature to conquer, fight and steal. It's not justifiable to say that we should do those things just because it's in our nature, so how can we apply that argument to other pursuits?