In any case, to be a backup, Mars would not only need to be economically self sustaining (in the sense of earning more than it cost), but it would have to be able to produce absolutely everything it needed to survive and grow, as Earth would no longer be available. Every material, every component. Everything. This means not planting a colony, but planting an entire global economy.
This is some Atlas Shrugged level nonsense. The presence of other humans is essential to making Mars habitable. The colony will need a huge economy just to make all the materials and things it needs.
Have you met humans before? Like, the humans that perpetrated the countless wars throughout history? Slavery, the holocaust? You think that animus has been exterminated or something?
Imagining that we're all going to be cooperative do-gooders because we all hang out on HN and love open source is the "Atlas Shrugged level nonsense." It'll be a mad house.
You'd don't get to conclude that having other people around is bad because there could be desperate people among them. Having other people around also delivers huge benefits, such as providing the gloriously diverse global economy that allows one to manufacture the Mars colony equipment in the first place.
I get a Galt's Gulch stench from some of these fantasies of Mars as sanctuary.