Interest or usury does have a beneficial purpose. It is important to any economy. Here's a simple analogy. Neighbor A has time but no axe, neighbor B has an axe but not the time or physical ability. Neighbor A borrows neighbor B axe with the promise to return the axe plus a share of the firewood cut. Neighbor A then chops wood, returns the axe plus the agreed upon share of wood, has wood for himself, and trades some of the remaining wood for an axe of his own. This was all made possible by the wealth already created and that wealth was magnified by the labor of others for everyones benefit. Investment/interest/usury has an important role to play in creating wealth.
The US dollar is traded in places the US government is not. The US government has most certainly disappeared from Vietnam, but I can still use dollars there. Not because of the US government, but because Vietnamese people are willing to trade for it. Get rid of the US government and US dollars will not disappear. They will only disappear if you replace them with something else. In this example, old currencies are exchanged for new currencies at the bank. They don't disappear, they physically are collected and exchanged for a new currency. For example, when we change to Euro's we simply use domestic currency as markers in their place until some Euro's are printed. Someone writes an E on the note in marker pen. Roman coins are anything but worthless. Last one I saw on sale went for thousands. Coins have scrap metal value and also value for collectors. They are still tradable goods. Their value as such is much reduced because most places won't accept them. Again although I see your point, the worth of this currency is only what another person is willing to exchange for it. The government will not exchange you anything for it. It does not guarantee your money. No one guarantees you your money. You trade for $10,000 and the value of it fluctuates. Currency appreciates and depreciates. Prices inflate and deflate and different people offer you different prices for goods and services. The same car from one person may cost you the full $10,000 and from another person only $9,000. One person may offer you $10,000 for your labours another only $5,000 The value of your money is defined between the you and the person you trade it with. No one else.
You can pay taxes with gold. You can pay taxes with anything of value. They prefer currency. We all do. Example. If you have no dollars to pay your taxes. A bailiff will be sent to your house/business to collect goods equal to the value you owe in $. Your tax bill will then have been paid.
Like I said You do not use gold to buy things And when you say you use gold to buy money That means that gold is not money Any more than a share in Netflix is money A share in Netflix is like gold in that either can be exchanged for money
A gold coin is money. It's a different currency sometimes. A Britannia instead of a Golden Eagle. I could exchange it for Pounds or Dollars or Euro's. You can buy money with money. I can trade it for stuff. I could have bought other things than cash in the shop I sold it. I have bought diamonds with them, platinum chains. If you can find someone to trade your Netflixs share with, you can trade that too. Anything can be a trade good, not just money. I can trade my labour for a chicken if I wish. Or lager!. If I have no money I can trade your netflix share for my labour or something else I own. If you want.