People need to think of MMT as the "relativity" of financial theory. It is not a policy; it is an explanation. Einstein wondered why certain phenomena defied Newtonian physics. Economists wonder why the Bush and Trump tax cuts did not cause inflation. The reason is that deficits per se don't matter; only the relationship between supply and demand matters.

Government spending without taxation can cause demand to outstrip supply, but if supply is growing because technology and globalization (itself a technology), the demand may not be able to keep up. That's why the large deficits in the US and Japan have not proved inflationary.

MMT changes the focus from fiscal balance to actual supply and demand. In the "traditional" fiscal responsibility ratio of deb/GDP, the denominator is a proxy for supply. MMT puts the relevant output gap into play by substituting potential global USD transactions for Gross Domestic Product as the measure of supply. That figure is difficult to calculate, but it is nevertheless the correct conceptual bogey, and the farther it gets from GDP, the more urgently MMT is needed to explain why we must nevertheless try to calculate it.