Sending humans is an intrinsic goal, worth accomplishing for itself. It's like producing a great work of art.
(You're wrong to think that the robotic missions can be justified instrumentally. The science being done by Curiosity is kinda interesting, but it's hardly $2.5 billion worth of interesting. We could do much more important science on Earth with that money.)
(You're wrong to think that the robotic missions can be justified instrumentally. The science being done by Curiosity is kinda interesting, but it's hardly $2.5 billion worth of interesting. We could do much more important science on Earth with that money.)