You can have transactions denominated in crypto using conventional database technology. This happens when people buy crypto using PayPal or Cash App or Robinho

You can have transactions denominated in crypto using conventional database technology. This happens when people buy crypto using PayPal or Cash App or Robinhood, and at least thousands of times a second worldwide on crypto exchanges. More generally, there is nothing stopping anyone from making a "PayPal of crypto" or a "Zelle of crypto." In my mind, this is no way defeats the purpose of bitcoin. Bitcoin is like a Euro but for the whole world (which would never be politically achievable), plus cannot be manipulated (in terms of supply and interest rates) by a central bank (I think a huge plus, but obviously this is controversial). The point of bitcoin is not to be able to do illegal things on a blockchain. Personally, I don't care about the other (i.e. non-bitcoin) cryptocurrencies. There's some interesting tech there that could change the world, but defi and smart contracts are addressing totally different things than bitcoin is.