First of all, it's not guaranteed that it'll say "not controlled by anyone". For example the arms race of something like bitcoin mining leads to mining becoming unprofitable to anyone not building massive mining farms. The efficiency of mining leads to bigger control over the proof of work so there's a natural centralization of control happening with proof of work. And proof of stake isn't saving anyone either because that just opens the door to a different kind of centralization of control. Give it another 50 years and currencies like etherium will also be centralized. With all of the negatives and none of the benefits of centralization.

And that's the other point, I don't think an internationally independent currency is that great of an idea. At least I don't think it's better than a currency with a central authority. For example central authorities manage the inflation (or in case of crypto currencies the deflation) of the currency to keep is stable and usable. Central authority also keeps oversight of illegal activities, the lack of that oversight is why crypto is popular with the black market. You also get certain consumer-protections which you're unlikely to get with crypto because there's no authority to enforce them, for example if your account gets hacked or stolen you're fucked while banks would freeze your account and reverse transactions. And of course there's taxation, which I can't imagine how that would even happen with crypto.

I'm not saying blockchain itself is a useless technology, but I have don't believe it's usable as a currency. I also have some serious reservations in its use elsewhere because I have a hard time imagining where it would be better than a traditional database solution.