But, if you fully trade using any of those examples as money, you're actually invisible to the tax collector...
My landlord doesn't accept turnips either. And he needs to pay property taxes regardless of whether or not I'm renting.
Do you live in a cashless society?
The only time I touch cash is:
1. When my girlfriend pays me her half for getting groceries.
2. Which I then use to feed the laundry card refill machine in my apartment.
Mind you, I don't want cash to go away, but yes, I essentially live in a cashless society.
You can't pay in Bitcoin or gold either, yet both are incredibly popular.
What is the annual volume of gold transactions, compared to the annual number of USD transactions? Hundreds of thousands, versus trillions? Is there anyplace in the country where I can pay my green-grocer with gold?
Describing gold as an incredibly popular currency makes alternative-facts look honest.
We're talking about a hypothetical cashless future, and your argument is that right now, this isn't the case.
...
And you're conflating store of value (Which gold is... An OK one) with currency.
A currency is a store of value, but a store of value is not necessarily a currency. Gold, as a currency, has terrible properties.
The US government also expects your tax payment on an annual basis.