How can you bring humans to Mars without also bringing human nature, i.e., human flaws? We'll wreck Mars quicker than Earth, because Mars is already a wreck.
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.