The reason MMTers (and I'm not a religious man, but I suppose that, in a way I have been converted) have to fight the Money Multiplier thing is because of this conversation:
MMTer: Public debt can be monetized, inflation is created by spending (public or otherwise) not by more reserves, central banks can control the interest rate independently of the quantity of reserves in the system.
Anti-MMTer: Wait, if you add reserves to the system, banks can lend more! That's inflationary!
MMTer: Banks can lend always anyway if makes business sense. Their only limit is the capital requirements of every particular bank. If lending makes business sense, banks can find the legally required reserves, they are not constrained by reserves.
Anti-MMTer: But the Money Multiplier!
MMTer: Facepalm
I wish I could remember in what book was the Terry Pratchett quote. It's a great quote.
I can't think of a single macroeconomist that would say "but the money multiplier" though. This is a straw man invented by MMTers to avoid debate.
Literally every single central bank's policies are designed and implemented by mainstream macroeconomists, as were the capital requirements. "Banks can lend always anyway if it makes business sense" is the system mainstream macro built. Of course, mainstream economists also consider the "if it makes business sense" bit (and to a degree the "capital requirements" bit) matters, and have models observing that the flow of money actually injected into the economy at a given interest rate being finite and relatively predictable, and they can make it go up or down in different circumstances by changing that interest rate. They also (since the 80s, at least) have a sophisticated enough grasp of inflation to figure that how the dollars are injected into the economy matters rather a lot.
MMTer: Public debt can be monetized, inflation is created by spending (public or otherwise) not by more reserves, central banks can control the interest rate independently of the quantity of reserves in the system.
Anti-MMTer: Wait, if you add reserves to the system, banks can lend more! That's inflationary!
MMTer: Banks can lend always anyway if makes business sense. Their only limit is the capital requirements of every particular bank. If lending makes business sense, banks can find the legally required reserves, they are not constrained by reserves.
Anti-MMTer: But the Money Multiplier!
MMTer: Facepalm
I wish I could remember in what book was the Terry Pratchett quote. It's a great quote.