Colonizing Mars is going to be easier than solving tragedy of the commons.
If one looks at the history of colonies (attempts to colonize the new world, for instance), we see that they often fall apart socially even in situations where they're in a place with much more resources than they had back home. Humans aren't dwarf fortress type automatons that can simply be handed whatever necessary job is needed and mindlessly go about their day for the rest of their lives.
No one has been able to manufacture a functioning mini-society, and every attempt has ended in spectacular failure. It seems crazy to think things will suddenly work if we drop the people in a place devoid of almost all resources and entirely hostile to life from Earth.
We don't know if human nature can be "fixed" (in a positive way), so stopping other things until that's been done sounds a bit silly to me.
What's the point of a "backup plan" when the primary plan isn't even working?
The whole point of a having a backup plan is for when the primary plan isn't working :S
c/when/if
When your primary plan isn't working, you fix that first. Ideally, the backup plan is never needed.
If your house is on fire, you don't start building a second house, you put out the damn fire.
Also, it would be pretty dumb to put a backup in place more dangerous than the original. It would be like building your second home inside a volcano.