A good understanding of Market Monetarism would have gotten you to the same place and without all the goofy ideas about the irrelevance of deficits and debt
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No, he's arguing that QE is inflationary under certain conditions and not inflationary under others. And he's pointing out that you're ignoring the differences. He's right. You can't indefinitely print money/debt under any and all circumstances and never expect and inflation
For MMT to work as advertised, the Fed would have to keep interest rates at zero indefinitely. Maybe it could do that. Maybe it couldn't. It's a dice roll