rYes tha's it: Why send humans to Mars?
The Moon is still as close to the Earth as it was during the 1960's, and Mars is still just as far away.
While humans are essential in some tasks, for other tasks the transportation costs outweigh the benefits. These costs can be so high as to actually result in diminished returns, and that currently is the case with manned Mars geology:
you could get them there, but only for a short period of time. The Mars Exploration Rovers have demonsrated the lengthy periods of time rovers can be operated for on Mars.
Some comments on diversion technologies really belongs to another post...