Is Manned Spaceflight Obsolete?

With new proposals for NASA on the table, it seems a good time to ask whether a manned flight to Mars -- the centerpiece of the Bush space priorities -- makes any sense and more generally whether sending people instead of robots into space makes sense.

To support human life, there has to be a whole host of systems added to the flight which takes space, time, weight, and lots of cash that could otherwise be dedicated to scientific instrumentation that could be taking meaurements and running additional experiments. What is the payoff for these costs? Yes, there are some things that can be done by people that we cannot do or at least cannot be done well without. And there is a cost to the image -- the public loves seeing people in space because it accords with our science fiction fantasies. But if the purpose of space exploration is science and more science is done by sending metal and no flesh, why spend money to do less science, just for a boost of the cultural imagination?