Why is remaining confined to a single planet framed as an existential imperative?

Answer

It leaves humanity vulnerable to catastrophic, extinction-level events

Proponents view remaining on one planet as leaving humanity vulnerable to extinction-level events, whether they stem from natural disasters or self-inflicted crises, necessitating a 'backup drive' for civilization.

Why is remaining confined to a single planet framed as an existential imperative?
goalSpaceXspace exploration