When primative humans or pioneers settled a landscape there was animals to hunt for needed protein and grasses to feed livestock. Neither grasses nor wild animals occur on Mars. No forests for lumber, no petroleum for fuel and plastics.
No infrastructure for production of goods. No distribution systems. We could live in self-contained biodomes but there are a lot of ways that could go. We would need a lot more than a few colonists to make things work, but then we would be putting more people at risk. What are you gonna do on your day off on Mars? Gonna go to the coast and watch the waves come in? Gonna go hiking on a forested stream trail to go see the waterfall? Gonna go birdwatching at the marsh?
I strongly agree. There are many problems with interplanetary travel and colonization that have not been solved. This is especially important:
What are you gonna do on your day off on Mars? Gonna go to the coast and watch the waves come in? Gonna go hiking on a forested stream trail to go see the waterfall? Gonna go birdwatching at the marsh?
One reason not to go to Mars that immediately came to mind was the presence of perchlorate compounds in Martian soil. In 2008, it was discovered that Martian soil contains significant amounts of perchlorate compounds, which can cause health problems even in tiny concentrations. Of course, astronauts will not be eating Martian soil or breathing Mars's atmosphere, but astronauts will be exposed to trace amounts of Martian dust unless complicated precautions are taken. Therefore, experts think that perchlorates pose a serious risk to manned Martian exploration.
As far as I know, Elon Musk's proposed manned mission to Mars does not involve any of the necessary precautions against perchlorate contamination. People have a funny habit of ignoring hazards they are aware of. Of course, his proposed mission was probably vaporware to begin with.