[Fitzcarraldo]

Humans can provide a "multiplier" effect to robots. Given a base of 10 human operators on Mars, they could direct 100 or more robots (rovers, aircraft, etc.) )without the Earth to Mars lighttime lag getting in the way.

[John H K]

The cost of life support, shielding, transport is so incredibly enormous the cost-efficiency simply isn't there. The same amount of money would be better spent improving artificial intelligence systems on unmanned rovers.

Planetary scientists interested in studying the solar system have NO interest in manned missions; in fact, they consider the manned space program a budgetary enemy; the Space Station sucking up money has already killed a lot of great science that could have been done with unmanned missions.

Like I said, people tend to approach this emotionally rather than rationally.

Look at the ENORMOUS improvements of Spirit and Opportunity over Sojourner. The improvements in the next set of rovers will be even more dramatic.