Why are human missions to Mars needed?

According to NASA, a manned mission to Mars is needed, because the real-time decision-making capabilities and spontaneous nature of humans can bring a new experience and perspective to the exploration of Mars that the robotic missions do not allow. Humans are more flexible, adaptable, and perceptive than current robots. According to Steve Squyres, an astronomy professor at Cornell University and principal investigator of the Mars Exploration Rover Mission, “we are many decades from robots that can match humans, even in the lab, and laboratory robotics is about 20 years ahead of space robotics.”

http://aerospacescholars.jsc.nasa.gov/HAS/cirr/em/9/2.cfm
http://www.marsdaily.com/reports/Are_manned_missions_needed_to_explore_Mars_and_beyond_999.html