The number of things that will kill Mars colonists is very, very long.

Until we can create a fully sustainable Earth-Like environment life on Mars will be short.

Humans are a part of the Earth. Literally. Surviving outside our biosphere is only possible when we bring enough of it with us. We are so far from understanding how much of "it" we have to bring that interstellar colonization is currently either still Science Fiction (for those of us that like to dream), suicide or homicide (negligent homicide at best).

We made it to the moon with the understanding that the round trips would be measured in days.

If Musk could build a sustainable moon colony I'd believe Mars is possible. Discussing Mars before the Moon has been achieved is IMHO standard Musk fraud. Promise something he know he can't deliver in order to pull in shittons of cash.