According to someone I know who works for NASA, the problem with sending humans to Mars is the amount of radiation they would be exposed to in the long trip to get there. Then the radiation they would be exposed to on the surface and then the same on the return trip.
The other major problem with exposure to zero gravity is actual bone loss, muscle loss and effects of zero gravity on our eye balls.
It is all the physical effects that would happen to the people, not the ability to build a rocket, send them and then bring them back.
This is what we have learned by sending people to the international space station for the last X years. FYI, the NASA employee that told me this is also a former US Air Force Lt. Colonel and now a member of the Air National Guard. He is a pilot and was a navigator and bombardier in the Air Force prior to joining NASA. He trained with astronauts that flew on the space shuttle.
Exactly. Unless we solve a series of very difficult problems, we will not be going to Mars. Then of course there is the trillion or so dollars you would need. Not going to happen. In America of old, maybe, but certainly not with the mess of a flophouse we have today.