True, but the assumption is that you'd get stuck on Mars with plenty of funding for supplies and reinforcements coming from Earth. Seems like a shaky basis upon which to plan such an extended vacation, considering we can barely keep an adequate supply of funding and supplies to everywhere on Earth as it is. Gambling that they'd be able to maintain a supply stream for the duration of my lifetime while on Mars is a pretty piss-poor gamble to make. Mars is no place to be when the supply ships suddenly stop coming because China decided to call in their debts and shut the whole thing down, or North Korea decided that shooting missiles at departing spacecraft would make for an entertaining fun-time activity.
A Mars colony right now would be such a hilarious over-extension of resources, you would honest to God have to be insane to even contemplate it.
I'd tend to agree with this. I feel like developing a sustainable colony in orbit would be much more useful. The advances toward space exploration rather than space colonization would be better and more quickly achieved just by advancing large space colonies rather than extra-terrestrial planetary colonies. You waste so many resources just getting to mars, and there's not even that great a garantee that it would even net much of a benefit.
A sustainable space colony is a much more significant step imo as that leads to sustainable space craft, which leads to long term exploration and the best garanteed way to spread the human species, which is the best way to protect the species from planetary scale disasters etc.
edit: Just to clarify a couple of my unspoken assumptions. A small human population with planned child bearing (even better if you could somehow control the sex of the child to be born), could maintain itself pretty indefinitely. A ship able to indefinitely support 20 humans while traveling should be able to travel near infinitely with some stops to repair wear and tear. I think that's a much more meaningful goal to have than to colonize other planets. A sustainable space colony close to earth would have hurdles also experienced by a mars colony, but would lack a bunch of the hurdles a mars colony would have (notably the resources spent traveling to mars).