What is the fundamental reasoning Musk cites for establishing a human settlement on Mars?
Securing a backup copy for humanity against single points of failure like natural disasters.
The fundamental reasoning behind the monumental undertaking of colonizing Mars is rooted in what Musk perceives as an existential imperative. Life on Earth faces numerous threats, including natural occurrences like asteroid impacts and self-inflicted catastrophes. By establishing a permanent, thriving settlement on another world, humanity creates an insurance policy against extinction, safeguarding the species against being entirely wiped out should a disaster strike Earth. This concept of providing a redundant system for human consciousness predates SpaceX's major successes and remains a core tenet of the entire endeavor.

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Elon Musk reveals 'vision' for Mars, plan to save humanity - YouTube