We're not talking about the same thing. You're talking about why the dollar will be stable (and I totally agree with you there). I'm talking about why you and I can do business in dollars, and that was the origin of the discussion: bitcoins are made for people who can't trust each other. With fiat currency we still don't trust each other, but we both trust a common third-party, and have good reason to trust it, at least on the "it will be there" side.