>The US dollar in particular has lost more than 90% of its value since abandoning the gold standard in the early 70s.
The supply and demand for gold have essentially nothing to do with real economic value.
Now, admittedly, you've drawn near to an actual critique of our current monetary system, but that would require you to critique capitalism itself, too. Here, let me do that for you:
Capitalism optimizes for the production and accumulation of capital. Therefore, the monetary base does actually matter, because money is the most liquid form of capital. Thus, capitalism will optimize society for the production and accumulation of money, however money is defined. Define money as some commodity, like gold, and you'll get people sailing across the world to rig up mining infrastructure and haul back a rock of zero ultimate worth, simply because that's the optimization criterion of the economy they live in. Admittedly, all that hauling and sailing does actually require getting something done, so you do see real economic development under such a system, but the same thing can be enforced with fiat currency via exchange-rate controls and the rest of the Bretton-Woods package (which was, in fact, deliberately concocted to make trade count more than finance!).
Whereas, in contrast, if you set the definition of money as being debt, your capitalist economy will become a debt-maximizing machine. Which is what we see now, since the early '70s when the capital controls, exchange-rate controls, trade regime, and gold standard of Bretton-Woods were all abandoned.
There.