This gold mining argument still seems a bit silly and perhaps circular to me. We use gold (a rare and difficult-to-mine substance) for the same reason we need Bitcoin mining: to replace fragile trust. If everyone were trustworthy, we could use shiny pebbles instead of gold coins. No resources would be needed to "mine" pebbles, you just pick them up off the ground. Everyone would be trusted not to pick up pebbles he didn't deserve, and only obtain them through trade or in some other socially approved manner (perhaps as a form of "guaranteed minimum income", every person would be allowed to pick up one pebble per day.
I think you're right. In a world where everybody is 100% trustworthy, pebbles are perfectly effective as a store of value (maintaining the global ledger). The fact that there's no competition to pick up pebbles beyond one's pre-defined allotment means that very little resources are consumed "mining" for this money. So this seems to weaken Andolfatto's argument.
So, if trust is perfect, no resources need to be consumed by "mining," whether money is digital or physical. I suppose the question then becomes, "given that trust is
not perfect, what system for money is most efficient?" I think you addressed this with your earlier comment:
But ultimately, as with anything, its only "wasted" if there is a better alternative. If you are going to use gold as a form or money (or even merely store of value) than it is essential that trust be maintained by continually trying to break it. This is very similar in essential, underlying function to Bitcoin's PoW. You can't declare (by "fiat") that the oceans contain no gold or that asteroids contain no gold, or that Bitcoin miners will nicely and fairly take turns collecting the free coins that are being distributed.
But it is true that if there is something else that is more efficient as a store of value than gold (like say Bitcoin), then mining isn't necessary. Indeed if that happens the price of gold will plummet, and mining will essentially stop.
Haha, I felt I was on the verge of some new insight. Maybe not...