Go back to my scenario: when you use a US credit card, denominated in USD, to buy something from a European merchant, whose prices are in Euro and who receives Euro from the purchase made, are you buying the goods in USD (the currency that your account contains) or in Euro (the currency the merchant receives)?

From the perspective of the customer, you only ever see the dollars: that's what your account contains and that's what the number that goes down in exchange for the goods. Yes, behind the scenes, your bank turns that into Euro (liquidates the gold for you, in your example) and sends the Euro to the merchant, so as far as the merchant is concerned, the transaction is in Euro, but from the customers perspective, everything happened in USD.

I'm not arguing that you're not correct, that you are technically buying goods in Euro, what I'm saying is that from the customers perspective it may as well be in USD.

For the cryptocurrencies, of course I'm technically buying in USD, on-demand liquidating the cryptocurrencies to USD in the process, but from the customer experience, I may as well be transacting cryptocurrencies and I am spending my cryptocurrencies (via a transparent exchange behind the scenes) to make the purchase, just like a USD card holder spends their USD (via a transparent exchange behind the scenes) to make their Euro purchase and just how you would liquidate your gold (assuming there was a "gold" visa card where the bank handled the liquidation for you transparently behind the scenes) to make a USD purchase.

From my perspective, when I use the Binance card, I am using my crypto to buy something. How that works isn't relevant to me. I don't see the USD[1], I see my crypto balance go down and I get the purchased item. For all intents and purposes, I am using crypto to buy things. If I didn't have the crypto, I wouldn't be able to buy things with that card.

What the customer sees matters, since the money in a non-gold-backed account is just a number anyway, you're not really "spending" anything. But from the customers perspective, the number represents the USD (or whatever) that's in their account. When they make that number go down, that's what they're spending. If the bank decides that for some reason its more efficient to convert the money to GBP first, then to Euro and then back to USD, good for them, it doesn't affect the customer. Its an "implementation detail".

Or another scenario: What if I use a USD card to make a Euro purchase, but the merchants account is in GBP? (A UK-based business with an EU-localized store, perhaps) I am buying in USD, the actual purchase transaction happened in Euro and the merchant only ever sees GBP. You seem to be arguing that only the middle bit, the Euro transaction, matters. I'm saying which part matters depends on the observer: for me, the USD part is what matters, for the bank the Euro part might be the most important and for the merchant its the GBP part. For all intents and purposes, I spent USD, the merchant received GBP, but the bank processed Euro. The dictionary says "spend" means "to use up" or to "pay out" (and pay is to give), I'm using up the USD in this example.

[1] I mean, technically I do: the merchant quotes their price in USD and Binance does of course let you see the USD equivalent balance of your cryptocurrencies