The problem isn't the marginal tax rate. The problem with MMT is that it takes, as its base assumption:

...that sovereign governments have an unlimited financial ability to pay for the things they wish to purchase and to fulfill promised future payments. MMT claims that these governments also have an unlimited ability to provide funds to other sectors, and that because of this, it is not possible for a government that issues its own currency to be bankrupt.

Fundamentally, it's an institutionalization of "too big to fail" - that it doesn't really matter if Moody's downgrades the debt of the United States which causes the price of bonds to go up which causes borrowing costs for everyone to skyrocket because the United States can always print more money and in the end, it doesn't matter where the decimal point is, it matters where the jobs are.

Now - it's important to note that nobody serious is saying "debt unending forever and ever amen". AOC and her 70% marginal tax rate isn't saying "let's spend money forever" she's saying "tax the rich and boons for the poor." But when Obama bumped the debt up something crazy in response to the recession, his spokescritters all had some variation of "debt is overblown" to soothe the talking heads with. "debt is overblown" is every bit as panic-inducing as "gay marriage bakery" and "death panels" to the 'wingers so they're getting themselves spun up into a tizzy over this whole "modern monetary theory" thing well ahead of anyone saying anything more than "I think it should absolutely be a part of the conversation" (which Ocasio-Cortez said to 60 minutes). Everything else she said? That's getting buried.

"You can pay for it by saving costs on expenditures that we're already doing," she said. "We can do it by saving money on military spending. We can pay for it by raising taxes on the very rich. We can pay for it with a transaction tax. We can pay for it with deficit spending."

"You recognize that people still ask the question as though I didn't just answer it," she told INSIDER. "Because it's not an interest in the actual answer. It's an interest in the attack and it's an interest in debasing the agenda."

Really, the Left is basically saying "European-style taxes" and the Right is trying to pretend they said "Laffer curve." But I think it's interesting that we're now in the weeds of "what is money, anyway?" considering Occupy Wall Street and the bank bailout is what launched Bitcoin in the first place. When finance is demonstrated to work differently for institutions than for individuals, individuals resort to alternative markets.