re: Even if Mars or the moon was covered in gold dust...
Right, but accentually that is the argument that the Moon folks are making.
That Lunar ISRU will make economic sense even when you add the costs of launch of equipment from Earth and the inefficiencies in the production of cryogenic hydrogen and oxygen and the storage, transporting it around on the surface of the Moon and then launching of it off the Moon...
This is the center post of their tent and suppose to be the basis of our return to the Moon and travels to Mars. Without ever running even the simplest prototype rover/extractor experiment here or on the Moon.
It makes more sense to explore lowering launch cost from here first than pinning everything on ISRU at the Moon.