I think this relates closely to the US govt's opinion that all those big banks were "too big to fail". A defecit that increases by 1 trillion a year is bad news. People are paying for this. The american public, the ones that save (lol), are having their money eaten away by inflation. That, or foreign investment is paying for it, and that just isn't sustainable.
Ok, you need to introduce some clarity into your thinking. You're obviously well read and keep up with financial news, but the way in which you interpret is perhaps a bit woolly (I'm not trying to be rude).
Firstly, the deficit to GDP ratio in the US is about 80 pct (more or less), so talking about "trillions" is disingenuous. It is a favourite trick of newspapers, as "trillion" sounds scary.
The deficit in Japan is around 190 pct, and their 10 year rates are 1.3 pct (and have been for a while). There are very clear differences in saving patterns in these two countries, but based on this data you CANNOT then conclude that the US debt is "unsustainable".
Second, the money we use is not backed. It is fiat money, with nothing behind it other than the legal structure of the country to enforce its usage. Even if you think the USD is worthless, it is still the legal currency in the US and must be accepted for transactions. As such, the central bank can always generate more money to replace that lost during asset price deflation.
(90 pct of "money" in circulation is created by debt, read about fractional reserve banking on Wikipedia).
Something is unsustainable though, and it has nothing to do with paper money. It's the human race's usage of resources. The US has 5 pct of the world's population yet uses 20 pct of the world's energy. They have a serious case to answer there.
What about in ten years time when everyone in China wants a car? THEN we are going to have real problems, and it has nothing to do with paper money, it will be all about natural resources. The likely outcome is war, which is usually the best method for reducing demand in the medium term.