You really don’t want the folks in power to have even more of that kind of power, no matter how convenient it is most of the time.
At least Visa/MasterCard, etc. mainly just care about making money. The gov’t doesn’t even have to care about that!
Using ‘we’re currently in a democracy’ to justify creating an even more tempting and likely to be abused tool of oppression is not a good idea.
In your hypothetical scenario of nazis taking the gov, lets assume there is no central database. Nazis would go: ok banks give me your databases or else. Banks gives databases because they care about money. There, now nazi have central database. And in this scenario you have deprived the people of enjoy a really nice service.
Where is the win here I don't see it. Let's not do good thing because, oh, in a doomsday scenario good thing might be bad. Like, shouldn't we channel efforts in ensuring doomsday never comes to reality in the first place? This way we all enjoy good life with ever improving services.
I’m also pointing out not-that distant past events, and you’re also just completely ignoring them.
Good luck! Just don’t do it in my economy.
The system works if democracy works. If we lose democracy, of course, the blocks built on top of it would crumble. That does not means everyone should stop building on top of democracy. Even more so for things that makes the life of the people better.