Sure, the shares are collateral. If their value drops, the brokerage will sell them to cover the expenses I racked up on the Visa card. But it's not like the p

Sure, the shares are collateral. If their value drops, the brokerage will sell them to cover the expenses I racked up on the Visa card. But it's not like the pizza I bought was priced in AAPL shares! It was priced in dollars. The margin loan isn't material to the payment system. It's the same situation with crypto debit cards. Anything you buy with such a card is priced in USD/EUR/whatever. The crypto behind the scenes makes no difference, just like the AAPL shares in my brokerage account. Hence these crypto-backed cards are not crypto payments in any sense — they're a financial product that already existed.