I can't buy my groceries with AMZN shares, and they're not intended to be able to do that. No one is pretending AMZN shares are going to be a peer to peer currency.
I can't buy my groceries with BTC either, but that's because no store will trust a payment method where within an hour the value of what I've paid them declines 10%.
Nobody is arguing about that. The idea that BTC is a currency is long gone. Bitcoin is a store of value, similar to gold (which you also can't use to buy your groceries).
You absolutely could use gold to back your personal economy. Put dollars into an InteractiveBrokers account, buy GLD. Use your IBKR debit card to borrow against your GLD on margin. Pay it off at the end of the month. You can back your personal economy with literally anything you want that way.
I can't buy my groceries with BTC either, but that's because no store will trust a payment method where within an hour the value of what I've paid them declines 10%.