It's a weak argument to suggest that robotic probes can explore space more cheaply and more effectively than can human beings. Robot probes have failed miserably for many tasks.
First, the failure rate of robotic missions is nothing less than bewildering. The incredible fact is, the majority of landing pods sent to other planets have failed, many catastrophically. For example, of 12 probes launched from Earth that were designed to land on Mars, 4 can ( charitably) be called at least partial successes, the rest failed utterly.
As for the "successes?" Well, the Mars exploration Rovers are rightly lauded as the last word in successful robot landers. I certainly concede Spirit and Opportunity have done great, even spectacular work. But compared to a human? Nothing less than pathetic. It took Spirit more than four months to traverse 600 meters. A human could cover that distance is a few hours, and know what it was looking at, to boot.
Robotic exploration enthusiasts often seize upon the failure rate of roboticized mssions and argue that it shows that manned exploration is too dangerous, and that robots should take these risks instead. Alternatively, the disparate failure rate is explained away by noting the vastly higher safety factors engineered into manned craft (with the attendant higher costs).
The trouble with these two positions is that many of these failures wouldn't have occurred at all with an actual, *thinking* human pilot aboard. Contrast the manual landing of Appollo 11 with the crashed Soviet robotic lunar lander days before. More recently, the DART (Demonstration for Autonomous Rendezvous Technology) Spacecraft crashed into the satellite it was meant to rendezvous with, a procedure that is routine for American and Soviet astronauts. So, too were the Mars climate orbiter, Deep Space 2, and the Mars Polar lander.They were all lost because computers don't adjust as pilots would have.
The fact is, until there is working artificial intelligence, there is just no substitute for men and machines working together.