A decent point but the government accepting payment in a certain currency requires that they are sure/believe that they will be able to use that currency to pay their debts. Same thing applies to the debt argument both rely on a communal acceptance that a dollar/euro/ruby/piece of eight/bitcoin/kongbuck will be accepted as payment.
I suppose it'd be clearer if I said it's exchange value is ephemeral, ie completely determined by the faith that currency X is worth/will be accepted in exchange for some amount of currency or product Y.
A decent point but the government accepting payment in a certain currency requires that they are sure/believe that they will be able to use that currency to pay their debts.
There are all sorts of ways to answer to this, but all of them amount to pointing out the bleedingly obvious: Most[0] governments issue debt in the same currency that they demand tax payments in, so your condition is not really a condition at all.
If somebody holds a government bond denominated in currency X, then they will be paid in currency X. If they suddenly decide that they would prefer to be paid in currency Y, well, take it to the foreign exchange: said government does not, and does not need to, care.
[0] The governments that don't do that almost invariably end up in trouble at some point because of precisely this. On a related note, almost all stories of hyperinflation are in fact stories about foreign-currency-denominated debt.
I suppose it'd be clearer if I said it's exchange value is ephemeral, ie completely determined by the faith that currency X is worth/will be accepted in exchange for some amount of currency or product Y.