It would be completely possible to continue quantitative easing until all of US public debt has been purchased. This would result in the only liability being issued as the monetary base. In other words, the federal government would no longer issue interest bearing debt. Milton Friedman actually proposed the same thing of all people.
This could result in being somewhat inflationary, but that could be easily remedied by some tax increases (even though QE to date hasn't made tax increases necessary). This would really baffle the Austrians and their various cult members. The economic illiterates would be completely baffled.
You are right and I think Friedman and austrians, even though they advocate vastly different policy than you, have understod this very well.
There is just a semantic difference. And by the way, I think MMTers use language that is in fact not in line what the system currently actually is. IE the treasury can't unprint money by increasing taxes. Or maybe it can but that won't practically ever happen in any meaningful quantity, even if they let the bonds mature the FED could buy something else and lower interest rates. What is collected in taxes is spent. That's the reality.
MMT explains monetary operations quite soundly. You said all taxes are spent. Of course they are. MMT simply points out that spending precedes taxation in the primary instance. For example, it would be literally impossible to collect tax $$$$ from the private sector unless it was spent into existence by the public sector. However, on a daily basis, the Treasury does receive tax payments, and there’s a daily clearing of government checks.
We can begin with spending, but it really doesn’t alter anything.
By the way, I’m not trying to engage in semantics. When MMT says “government”, they mean the entire central government, such as Congress, the Treasury, the “independent” bodies like the FED, etc. We should understand that the system is made up of these institutions and they were created by Congress. This means they are subject to regulation by Congress. This where the consolidated government sector comes from.