The case for using the blockchain for currency (if you want to call it that because the existing cryptocurrencies tend to act quite poorly as useable currency, they’re more like a commodity) does exist.
It’s usually not the ones that you hear crypto-bros talk about. Crypto-bros come in two flavours, they’re either clueless and are unknowingly doing the dirty work for someone who is not clueless, or they’re lying to you about their true motives and goals. Either way, don't pay too much attention to what they say.
I can’t be arsed right now to go into a full description of the pros and cons of Bitcoin, Ethereum, Dogecoin etc. etc. Perhaps another day. Besides, this article is mainly about something entirely different, a Central Bank Digital Currency (CBDC).
A CBDC is essentially a form of digital money like we already have. Most people barely carry coins and notes anymore, it usually sits digitally in a bank account. Like a digital IOU from a private company to give you the equivalent value in coins and notes if you ask for it. Those coins and notes, in turn, are an IOU from the Central Bank that has created the coins and notes, to give you the equivalent value in something else. Think: gold or something. This is so theoretical that it barely matters what they would really give you in return.
There is something funny happening in the above paragraph. A public institution like the Central Bank makes the money for the people but it actually has no real relationship with the people. Except for oversight of course, Central Banks are usually operating within boundaries set by a democratically elected body such as a parliament or government. But that is as close as you and me get to a Central Bank. In real life we tend to rely on private banks instead.
Our employers don't give our salary to us at the end of the month, they send it to a private bank of our choosing who will keep it for us and displays their IOUs to us in the form of a balance in a banking app. We rely on private banks to be truthful about what they keep for us and to always be there when we need access to our own money.
That system with its curious split between public and private banking has worked well for over a century until the Global Financial Crisis of 2008. That's when it suddenly became clear that even private banks that are worth billions could suddenly collapse because of a lack of trust. When it suddenly became hard for everyone to assess value of things, the actual value of things could magically disappear. Safety funds had to pay out, people lost chunks of their savings (haircuts) or their entire house (foreclosure), Governments had to step in to save 'systemic' banks. The super brains went looking for ways to better weather a similar storm in the future. Some of them think they have found it in CBDCs.
One of the things that a Central Bank Digital Currency (CBDC) can do is, for the first time ever, create a direct relationship between a member of the public and the public bank. It is explicitly not meant as a replacement for private banks, it's meant as an additional bank account that you and me can hold with a Central Bank. There may or may not be some benefits to having that separate account in normal times. It's in times of crisis, however, that it suddenly becomes vital. Central Banks don't go bankrupt like private banks do. Let's say there's a major crisis (financial crisis, a war, a pandemic) and a government decides it wants to give money to everyone (whether 'helicopter money', 'stimulus checks' or whatever form) then putting it straight into people's account at the Central Bank is much easier and safer (putting helicopter money in a bank that might be about to collapse doesn't help the government or the individual) than using private banks.
Why do this on the blockchain? Because having a permanently immutable ledger does some times have benefits. And a better designed blockchain with this specific goal in mind can prevent the negatives of most money-on-the-blockchain (deflationary, high energy use, cumbersome, expensive) projects.
Anyway, if this piques anyone's interest, I'd start with what the Bank of International Settlements (an industry association of Central Banks, if you will) has published about it. BIS: Central bank cryptocurrencies. The ECB has published some interesting stuff about a digital euro and China has already launched one: China’s digital yuan is a warning to the world.