First of all, I don’t think there’s anything that can be titled “gold theory” per se. The policy question you bring up is, however, one of continuing to use the USD or switching to a commodity-backed form of currency, with the ideal commodity being explicitly recognized as being gold. But to understand which one is a better currency simply for Americans (ignoring the costs borne by the rest of the world), we have to look at what potential advantages come from using the USD and what the nature of those advantages is, because I think you will see that those supposed advantages of the USD are neither stable nor desirable once the effects of the instability of using the USD manifest themselves.
After WWII, the US emerged as a world superpower and as the leader of the Western World. This, as you say, was the advantage of a life time. It was decided at Bretton Woods that the USD would be the “key currency” in a new international monetary system, where the USD would be backed by gold (yet redeemable only to foreign governments, not citizens) and foreign currencies would be backed by reserves of US dollars. The supposed advantage of using the USD in the United States was simply this: because other governments needed US dollars to back their own currencies, the US could essentially export dollars in exchange for real goods and services from abroad. It seemed as though we could get rich simply by printing money, because the new money would be sapped up by foreigners so that we wouldn’t have to deal with inflation at all. Virtually free imports! That was the promise of the Bretton Woods system for the United States.
However, we must recognize that this system could only persist when foreign governments desired more US dollars for their own currencies. As Americans continued to increase the supply of US dollars, and as many of these dollars were exported, the inevitable effects of inflation eventually started to be felt as the increase supply of USD decreased the value: increasingly, foreign governments were deciding to hold the US government to its promises and to redeem their US dollars for gold at $35 an ounce.
This is where you fail to recognize why Nixon abolished this system: it was not true that inflation didn’t threaten the future of the USD before Nixon cut the ties to gold, it was precisely because inflation was threatening the USD that Nixon abolished the last link to gold. Because foreign governments were increasingly calling on the US government to redeem its US dollars, the US reserve of gold, and thus the base of the USD, was being threatened. Nixon’s choices were either to stop inflating the money supply (and potentially even to have to contract the money supply) in order to maintain the United States’ gold reserves, or to break the link with gold altogether. He choose the latter course of action, as history shows.
And here is my crucial point: simply because the US has a monopoly on the production of US dollars does not mean that there is always going to be a demand for US dollars. As the supply of a fiat currency is increased, it is valued less and less, particularly because a fiat currency is valued only because of its marketability value, rather than any real use value. People will gradually expect the value to decrease, and will want to decrease their cash-balances of that particular currency, thereby further decreasing the value of the currency. Eventually, this process leads to hyperinflation.
So while the US may have had a great run getting people to demand the USD, because of the nature of inflation, there will eventually be a point at which people stop demanding more USD and start trying to use them to purchase US goods and services. However, with the increase in nominal demand for US goods and services, US prices will start skyrocketing, thereby encouraging more people holding US dollars to spend them in the US while they still have value. When this point comes, the USD will be finished. And the longer we rely on people to keep sapping up our dollars, the worse this crack-up boom will be, and the more everyone loses.