alt Hacker NewsMars is not a safeguard against Earth going to hell, even in the most extreme Mars fantasies you don't end up with something independent of Earth for an indefinite period of time. We're also more than capable of exploring our Solar System in immense detail without sending people or colonists. Our greatest achievements on Mars have involved rovers, and frankly suggest that as a planet it has little to recommend it.
tl;dr There is no reality in which it's easier or more reliable to "back up the species elsewhere" than it is to act in our interests here. That doesn't imply shutting ourselves off from space, but it means treating it more like the deep ocean where rovers and drones are simply a better fit for such hostile environments. I'm hopeful that will change someday, but anyone who's thinking in terms of decades doesn't understand the scope and depth of the problem.
My recommendation is to read some of the books and articles suggested in this thread before imposing your wishes on reality.
As noted in the original post, I don't really buy into the "backup" theory so much. It's more that it would be a shame to have gained the ability to put people in space and then lose it having done practically nothing with it.
> I'm hopeful that will change someday
And part of my point is that these things don't just magically change on their own, but because a lot of smart people are actively working on changing them. Absent those efforts, the status quo remains.