In the parents defence, the tax status of crypto has nothing to do with the technical capability of using Bitcoin for trade. I think we can all agree, that if both parties are willing, I can use bitcoin to buy things.
Visa: get card from wallet, type in number, type in CSC code.
Cryptocurrency: pull out phone, scan QR code.
In the US you can get a 2% rebate on what you spend with a credit card. In effect, you are credited back most of the merchant fees baked into transactions.
In which case cash or crypto requires a >2% discount to break even.
I completely agree that the instances of use as currency is vanishingly small.