The problem is that there is no economic case for ferrying stuff to and from Mars. There is nearly nothing on Mars that anyone on Earth will pay a premium that will pay the costs of colonization off. It's the ultimate exercise of ditch-digging, and ditch-filling, with the justification that doing so accelerates the technological development of ditch-digging instruments. Which is both technically correct, and also completely insane.
I don't think it's obvious at this point whether or not a Martian colony would be profitable. A lot depends on technology and costs. Transportation costs are the biggest hurdle at the moment.
Any potential Mars colony is likely to be populated by an early group of scientists and tourists, but there are a lot of other reasons people might want to visit Mars or stay there. Mining of high-value minerals. Filming TV shows and movies. Sports. Claiming the best real estate before someone else does. Establishing a refueling station between Earth and the asteroid belt. Manufacturing heavy space equipment that we don't want to lift out of Earth's gravity well. Some people with mobility issues might rather live in low gravity on Mars than be bound to a wheelchair on Earth. And so on.
