When I talk about this "theory," I am very specific about how the federal government finances itself RIGHT NOW. There isn't much about MMT that is theoretical.
Other schools of thought, that said QE would lead to massive inflation? THAT'S theoretical. When MMT said that QE would not lead to massive inflation? THAT was theoretical. (QE didn't lead to inflation, btw, so we were right on that.) Whether or not these plans will preserve the economy? That's theoretical stuff, and what I was hoping we would be discussing eventually.
But the mechanics of federal funding are objectively verifiable facts.
QE can lead to inflation, if the new money exceeds production to a great extent, i.e., if it's overdone.
If demand sinks, and it's use to bring demand back to normal, it won't cause inflation.
In the current situation, it probably won't, it will just prevent deflation if nothing is done. However, they could over do it.
The last QE that didn't result in inflation is not proof that QE doesn't cause inflation, for it has, in the past, so it depends on what is going on in the economy.
Quantitative easing - Wikipedia
Quantitative easing may cause higher inflation than desired if the amount of easing required is overestimated and too much money is created by the purchase of liquid assets. On the other hand, QE can fail to spur demand if banks remain reluctant to lend money to businesses and households.
This is my beef with MMT'ers, it's becoming a cult of sorts, as if this is the panacea for all of our economic woes. The truth is, it's considered "fringe" economics by many economists, though no one is doubting that a few persons of letters are advocating it.
My criticism is that they, like you, offer the last 10 years as "proof" that QE doesn't cause inflation. You have to go back further, a lot further, than that, to weigh the policy and know when you can do it, and when you can't, and even then, the economy is a very difficult thing to manage, because the effect of policies often take months to take affect, during which time the ground can shift again. Managing the economy is a tricky business, for sure.
I would be very reluctant to accept any school of economic thinking as the final approach to any problem, everything should be considered, and weighed, accordingly.