You're right on the second half, I don't think the US will default.

But to say the US$ is a stable investment is ridiculous.

Lets say I sell you 100 "Clinton Credits" for $10 each. Then you loan me 100 "Clinton Credits", with the expectation I pay you back 110 "Clinton Credits" at the end of the year.

Meanwhile, during the year, I redefine "Clinton Credits" so they're only worth $1 each.

I pay you back your 110 "Clinton Credits" at the end of the year, which you can then trade in for an 89% loss.

This is not a stable investment.

A promise to get repaid in fiat currency isn't really a promise if the lender controls the value of it. The only thing you can be sure of is that if you get paid back rubbish money everyone else will.