In its current state, Mars would be settled with environmentally sealed habitats, and likewise any humans wandering outside on its surface would be suited up. This means that decontamination procedures would apply to personnel and equipment returning from the Martian environment, as well as to personnel and equipment entering it (which is what should be done until the question of native life has been settled).
This
article goes into more detail. My take is that the presence of perchlorates on Mars is an additional complication, but not a show stopper. It's also kind of balanced by the fact that this means there's effectively a lot of potential rocket fuel on Mars.