Is this not taking a literal interpretation of his words a bit too far? Is your scenario really that because someone can stick their hands in their pockets and refuse to take the US dollars (and then a court declares that the debt has been paid), they didn't actually HAVE to accept US dollars because they can just stick their hands in their pockets? By that reasoning, I don't HAVE to not murder people, you can't make me, it's just that the courts will put me away for life. The whole conversation becomes meaningless.
Well, no; the point is that the legal tender status of US dollars is only relevant if and when an outstanding debt becomes the subject of litigation. How often does that happpen?
Further, an agreement could say something to the effect of "borrower will repay lender the sum of $1000, or 50 BTC", stipulating an effective exchange rate that makes repayment in dollars entirely unrealistic.
