Like I pointed out elsewhere, there's no more reason for a city on Mars to be any more self-sufficient for its every need than Las Vegas is. Cheap transportation is the key.

The "self-sustaining" thing is kind of a straw man unless you're talking about an interstellar generation ship or something.

If millions of human beings can live cheek-to-jowl in places like New York City with only a tiny fraction of them killing each other, they can probably do it anywhere.

In "Caves of Steel" Isaac Asimov postulated a future culture where humans were so comfortable in crowded underground cities that they were terrified of open spaces. Asimov contrasted this with a space civilization that had so few people in so much area that they were reluctant to have any personal contact at all.