People like to bring up places like Argentina and Venezuela, but their debts weren't denominated in their own currencies, so they had to collect dollars in order to repay debts in dollars. As a currency issuer, since we create dollars, we can never run out of them. Nor do we have to round up dollars and take them back from currency holders before we can repay a debt. Doing so just takes those dollars away from the non-government so that the issuer can zero out a ledger somewhere. The interest is interest we choose to pay, for some reason. The only way we could default on our debt is if we decide to. The only way to "pay off" the "debt" is to take all the dollars away from the non-government, which is _us_.
> The interest is interest we choose to pay, for some reason.
Perhaps this is the best point to talk about, because the precise way in which it's untrue is very concrete. The US government doesn't choose how much interest it feels like paying; it sells securities which promise a specific payout schedule according to an auction-set interest rate. If investors want to buy at a high interest rate, there's no mechanism for the government to demand they accept a lower one.
I think the popular misunderstanding is more harmful than some of the misunderstandings you point out (which some people may indeed have) because it leads to people pushing austerity because of their monetarist dogma.
Nobody ever asks who's going to pay for stuff when it's so-called "defense" spending. But if we want health care or education then it's all apoplectic "debt, hyperinflation, enslavement of future generations, where's the money going to come from!?"
Just look at Panama this very week. They were threatened to be invaded if they didn't give up economic deals with China and go back to being a servant colony of the US.
The odds of citizens cashing in and demanding all their money at once is pretty slim. The odds of countries that hold US debt doing it are better. But there's a strong deterrent for countries doing that. And it's the reality that the US has no issue with invading, and they've done it countless times this past century to the applause of the voters.