I cannot recomment strongly enough reading David Stockman's cogent exposition of how MMT is already here:
MMT is just another egregious form of fiat money. I have come to believe that human primates are not sufficiently self-controlled to handle the ability to print money without abusing it in extreme ways. Money based on metal provides, historically, stable prices, and hence removes the impetus for ever-increasing leverage (to get rich quick). The proponents of MMT on the left would use it to promote social welfare, I agree; but the Fed has beaten them to it, to promote welfare for bankers.
As to the critique that metal-backed money creates too much instability, two points:
First, fractional reserve banking existed during the gold era, and yet prices were stable on average over long periods. To my knowledge, this effect hasn't been totally explained. To dispense with the assertion that modern, post-1971 monetary policy created a "great moderation," no, it created a great debt bubble, as spending went further and further beyond income.
Second, the very idea that the business cycle should be stabilized is suspect. People should be stabilized. Most cyclical adjustments (or even more so, structural adjustments) need to be made; and "stabilization" policy simply masks what needs to be done, and generally prevents progress from being made. For example, preventing bad debts from being charged off rather than being put on the backs of taxpayers (around the world, as our model has been copied).
People in transition should be stabilized. People are in fact any nation's greatest resource. They should be kept healthy and offered transition assistance or at least a basic income.
What we are learning is that "stabilization" has been coopted on behalf of the haves, the have-nots don't have enough money, and aggregate demand and human capital are collapsing.