> It's one of the ways fraud is combated, for example. I seriously doubt it's fundamentally a technical limitation of the technology used, but rather a choice.

I know the payments industry pretty well, and I can assure you that the limitations of ACH are NOT a choice in the least. It’s a system that was designed in the ‘60s that hasn’t changed simply due to institutional inertia.

> But as you said people aren't doing this with BTC -- and if they're not, then this removes one of the use cases that would warrant it's value, so you're only arguing my point.

They’re not doing it yet, but just this week we’ve got MasterCard, Visa, and Morgan Stanley announcing their plans to support cryptocurrencies, especially on the merchant-services side. Supporting this does not remove the existing value, it simply reinforces it. Just like the US dollar, you can either transact with people purely on trust-driven centralized services (and enjoy the convenience that such services allow) or you can “withdraw” some of that “cash” and “mail” it to people in a trustless way (albeit very slightly less conveniently).

> You also seem to forget about checks

Checks only partially solve the problem that I described. First of all, you can't take a check and chop it into pieces and use those pieces as tender; you have to cash the check eventually. In contrast, you can spend the Bitcoin you receive to anyone that willingly accepts it either in full or in part.

Second of all, while checks provide the functionality that "mailing cash via USPS" provides, it's equally cumbersome. If I want to donate $$ to a political dissident that's been canceled off of every platform, it would be quite annoying to find my checkbook, write the check, and then send it to that person. If I wanted this to be a recurring donation, it'd be even worse. That brings me to the next point...

> no one ever sends bricks of cash in USPS unless you're a drug dealer running a YOLO life. But you also ignore ACH/wires/credit cards and all the ways most money moves today. What is the fundamental issue there that Bitcoin solves?

The fundamental issue that this specific use case solves is that it allows one to transact with people even if the traditional rails disallow it. For example, if you want to donate money to your favorite porn star on PornHub or OnlyFans, it's impossible to do that via Visa/MasterCard/Amex/PayPal as these financial institutions have all blocked such services. Or perhaps a somewhat more topical use case: if you want to use and support services like Gab or Parler who are effectively persona non grata in the tech world, there is essentially no way to do this via the traditional payments rails. Crypto solves this problem in a way that's relatively more user friendly than mailing cash or checks.

If you lived your life on cryptocurrencies, you could transact day-to-day using your Visa branded card at your coffee shop (eventually settled on the blockchain), or you can “withdraw” some “cash” into a separate wallet and set up recurring donations on-chain. A few hours of automated asynchronicity is far less cumbersome than manually cutting, writing, and mailing checks every month.

> You're right, however regulations exist that enforce institutions use USD. Those are largely good things.

Correct, and in the worst case, it’s good that we have a fallback legal tender! But it’s also good that there are now more options in addition. With pegged stablecoins, it’s becoming easier to interoperate with USD.

> Being global means there's no local way to adjust things to current circumstances. Just look at Greece in the EU -- because they went on the Euro, with a totally different economy than Western Europe, they got all of the deflation with a GDP that couldn't keep up, and as they piled on the debt they didn't have any levers to pull. Unifying global currency is a terrible idea when you have very uneven economic realities around the globe.

I think that there are several assumptions baked into this argument that won't necessarily hold true. First of all, I don't think anyone believes that there will ever be one and only one global currency. Instead, the paradigm that's being challenged here is that, at a local level, you might no longer be forced to use one and only one currency. In the "new world" you might imagine a market of currencies with the option to use whichever you want to. If you think your government is being callous with its monetary policy, you can seek refuge in other currencies with little difficulty and even coexist with others that use different currencies. A lot of the new decentralized finance applications seem to be focusing on providing interoperability between multiple blockchains (Uniswap, Cosmos) as well as fiat currencies (via pegged stablecoins).

I think you're right that it remains to be seen if any of this will succeed or come to pass, but it's too early to say that it will fail. We're either in the mainframe era of cryptocurrencies, or we’re in the Concorde era of cryptocurrencies. Impossible to know which it is, at this moment.