Getting matter out of Earth's atmosphere and gravity well is expensive and dangerous. If we were to mine the moon, we'd have an abundant source of raw materials to build ships that can go elsewhere while not having to engineer them to deal with an atmosphere or a significant gravity well. Additionally, the tunnels that would be a byproduct of mining operations could be made into living spaces, offering free shielding from radiation.
Methane is quite harmless in the absence of an oxidizer. As it is underwater.
A six-pack of domestic beer at the State Liquor store costs $14. Free healthcare, indeed.
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