You're being careful to say that you know it's possible to put people on mars, but you seem to be arguing that it's fundamentally impossible for them to stay there for the long terms. You seem to be suggesting that faster than light magic is more likely than us figuring out how to manufacture greenhouses on mars. Do you really believe that closed cycle life support is so massively difficult a task that finding new physics and building the starship enterprise is a better hope?
Yes, mars sucks if you have to go out on it without protection, and yes setting up a self sustaining colony would be difficult, dangerous and very expensive. I'm not suggesting that we do it all right this instant. But everything that is necessary for human life could be manufactured on mars, and the tools to maintain that capability could be built there too. The more manufacturing centres you set up, and the more diversity there is among them, the more robust it becomes - tools existing to repair or rebuild other tools, exactly the same way we maintain stuff over here on earth. I am well aware that it would represent a really vast quantity of machinery to achieve all this, but I still think it can be done.
Again, I'm not saying we do this anytime soon! In the short term we do need to figure out how to live on just one planet, but over the course of a century or more it makes sense to start work on a permanant human settlement somewhere off earth.