[anthony_r]

Yeah, that's what I don't get: if you're going to invest effort and energy into reversing the oxidation of some element, why not choose carbon and decompose CO2? It will require non trivial amounts of energy either way.

[mkl]

There is very little CO2 on the moon, so that's not really an option.

[rendall]

Humans, livestock and industry will introduce it.

[politician]

It’s better to get a metal for the effort.