I agree with your risk analysis. Destroying civiliasation by ourselves is much more likely, it even happened several times, humanity still survived, but now we

I agree with your risk analysis. Destroying civiliasation by ourselves is much more likely, it even happened several times, humanity still survived, but now we have weapons which can fuck up whole planet much more thoroughly. BUT we can still insure against more than one scenario. Having home on another planet seems easier than changing whole humanity so we should at least try.