[vec]

The thing about dollars is that I can pay my taxes with them.

Let's say I think dollars are worthless, and my whole community works off something with real value, like shiny rocks. I'll still have to pay the IRS next April. They may take shiny rocks, but instead I could trade just one or two rocks for a big pile of worthless dollars and get Uncle Sam of my back for next to nothing. Unfortunately for me, every other shiny rock user in town is going to have the same idea, so they'll bid up the price of dollars until trading rocks for dollars doesn't feel any better than just paying my taxes in rocks directly.

The only faith that "full faith and credit" requires is faith that I'll have to keep paying taxes.

[lurr]

You don't think the fact that the other 99.99% of the population is perfectly happy using dollars is more of a reason?

[vec]

No, although that is nice.

Taxes are why I think a piece of paper with a bad portrait of George Washington has some intrinsic value to me, whether or not there's a secondary market for them. It's why I think the purchasing power of that piece of paper is anchored to a real phenomenon in the real world, and why I don't expect that purchasing power to move around much.

Think of it like this. If the dollar lost 20% of it's purchasing power overnight, I would be pretty damn sure something important has happened in American governance. Bitcoin just moved 20% because...?