That seems ... very far off. I dont necessarily disagree with setting a science mission up on Mars, but i'd strongly disagree with the notion that Mars is even a top priority for a diversification of baskets.
Also, the sooner you can get to Mars more reliable and more cheaply with larger payloads, the sooner that becomes a reality. Even if it never happens in my lifetime, that doesn't mean I think it's not worth working towards making all those things more real so it can be a reality at some point in time.
> i'd strongly disagree with the notion that Mars is even a top priority for a diversification of baskets.
Without even knowing specifically what you think would be a better choice, my guess is that cheaper, more reliable launch capabilities with bigger payloads will help that too.
So where's the better choice for redundancy?
> The difficulty, expense, and risk of setting up life on Mars absolutely pales in comparison to cleaning-up life on Earth.
First, that's irrelevant, as a sustainable colony on Mars provides something that you don't get no matter how much you clean up Earth. It can be pristine, it still doesn't get you redundancy.
Second, I don't think it's true that the price is so far in that direction. Cleaning up Earth is monumentally expensive as well, depending on what you even mean by that.
> Suppose there were a Mars colony. How many years before that colony could go on indefinitely if it didn't have support from Earth?
Sustainable in that it can produce the materials needed for modern living? I very long time, I imagine. Sustainable in that it provides enough food and water that a group of people could survive without having to worry about modern conveniences? Much less, and that's always got to be the first step, so that's what we go for.
Even if people on a mars colony ended up living a more simple existence in the case of the loss of Earth, that's still a chance for them to advance and continue that wouldn't exist with the world ending disaster on Earth.