The whole point of flat money is too simplify all variables and components pertaining to a normal standard of measure.
If we were to use gold...why not wood?, why not water? why not something more rare and expensive like rhodium?
What you want is simply no difference than organized battering, which is barely one step up from bartering whatever as value.
Flat money simplifies things, because it maintains money as a symbol of transaction of barter. Rather than having to complicate business by arguing over what the true value of each item is, you can come to common values and simplify the system so that you can maximize and maintain wealth across a system.
Additionally comes the problem of free market. In theory, if you can cause consumers to spend enough and reacquire enough money for their equivalent work, you eventually come to a stage where everyone can acquire anything, and thus maximize quality of life.
Having a limited system such as a physical material to express value, prevents a societies ability to achieve this stage of free market, perpetually preventing humanity from ever maximizing quality of life. Additionally achieving this theoretical height, would also result in the progress to maximizing technological, medical, and any other advancement known to man.
Think of it in these terms. If one has the efficiency to maintain a positive economy in this sense to near infinite heights...everyone would be equiavalent to a billionaire, who had to pay less than a cent for even expensive things such as extensive surgeries.
Now, theres theory and reality. While I doubt we will likely ever achieve THAT enormity of market ability(or at least not for billions and billions of years of evolution to a being new entity altogether)...a lesser comparison is still possible.
However, the problem is, the function works in its opposite as you fall. For each step you take up, each step down is considerably worse than the one below it. So if you have a massive decrease in efficiency after achieving such a height, think of it as someone opening up a whole case of whoopass on the world economy. Much worse than anything we could ever possibly imagine.
That is simply the way it is with money and market.