By the same token "we don't want to be defeated" isn't a good reason to create a planetary exploration timeline driven by false urgency. Mars isn't going anywhere.
And yes, Mars is not going anywhere, but the same cannot so confidently be said about our ability to get there. Our species has been capable of spaceflight for a tiny fraction of our existence and there is plenty of precedent for catastrophic loss of knowledge and capability.
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.
> 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.
In the case that we don't lose our ability to get into space, cool, development in that field gets a bit of an earlier start. If we knock ourselves back into the Stone Age, well, at least we can say we tried our best in that small window of time. The worst outcome is losing the ability without having even tried.