Lemme ask it this way.
If I were to hand you a dollar, how would you tell whether it was worth a dollar or not?
Okay, I get you now I think. Dollar is only worth a dollar because the government says it's worth a dollar. If the dollar was only legal tender to pay taxes that would give the dollar worth.
Look up the Isle of Mann or New York State before the state ratified the Constitution. Both use paper money as legal tender to pay taxes only. Both have or had in that of NY a viable paper currency that had value.
I realize Barak, under anarchy there would be no money other than gold/silver but the reality is that most people want a paper currency guaranteed by a government. I know that's stupid but its reality.