I am convinced that the first stage of colonising Mars should be orbital space stations rather than land bases. The vacumn of space seems like a far less hostile environment than the surface and one that humans have experience of from the ISS.
Any long term base on Mars is going to require constant resupply from Earth. So why not leave as much as possible safely in orbit, and make short excursions to the surface when neccessary?
The problem is radiation from solar storms. There is no protective magnetic field. On the ground, it is possible to go underground for those periods, in space, not so much. There is no light-weight option for shielding all that radiation, and being exposed to all of those your whole life is really bad.
Any long term base on Mars is going to require constant resupply from Earth. So why not leave as much as possible safely in orbit, and make short excursions to the surface when neccessary?