Earth stops being perfect after a rock hits us. This has apparently already happened more than once, and there's no assurance a breeding population would surviv

Earth stops being perfect after a rock hits us. This has apparently already happened more than once, and there's no assurance a breeding population would survive. I agree wiping ourselves out is currently the largest risk, but in the limit, we can always make redundancy with uncorrelated failure modes less risky than a single point of failure.