how long do you think it will be until we run out of gold?
We'd never run outta gold. As it diminished in available quantity, like everything else, it would go up in price. Until it was too expensive for people to want to trade dollars for. The link between dollars and gold never had to but static and set for all of eternity to be useful. But there had to be some kind of official relationship to protect people who owned dollars from what is happening right now.
But that's precisely what gave the dollar its power. The willingness of the fincancial establishment (as perscribed by the Government at the time) to trade, at any time, those pieces of cloth/paper, for something else that was rare and hard to create. When dollars=gold, then its not likely that people would rush to exchange dollars for gold, because dollars are something you can have confidence in, and are certainly more convenient.
Your argument that a thing is only worth what someone else will pay for it, is basically true. But the argument for gold goes to the fact that the alternative is terrible.
The true anchor of money is NOT the commodity behind it.
If the anchor of money is not a hard commodity behind it...then what shall it be? Is there one at all? Money is indeed a bridge for goods and services, but in order to function in that capacity it must relate in some meaningful way to the two. That's the point of gold (or oil, or silver etc...). That's the way in which it relates.
You don't need gold to anchor it.
You could anchor it to Big Macs.
Yes, I suppose we could anchor it to those. But now you've changed the argument, because a currency guaranteed in Big Macs (or anything else for that matter) is not a fiat currency.
That's the point and the central weakness of fiat. You're not guaranteed any amount of any commodity at all. There's no set relationship between fiat dollars and anything else, and as such, it is dangerous and unstable, as history testifies to.
Gold has served as the default currency for millenia because it is rare and hard to obtain. It represents the effort and work it took to mine/purify/or otherwise obtain. Now dollars, on their own, not representing gold...how hard are they to create? The government creates them at will to cover it's own financial melfeasance, so I'd submit that it's not hard at at all to create an excess of them.
I'm sure you know already what an excess of dollars means to those of us who have our wealth stored in them.