I think arguing "but it's a democratic monopoly" is little comfort in this situation. Maybe you trust your government not to ever be incompetent or to use the powers granted by this monopoly in a way you disapprove of. Maybe in the short term you'd even be right to do so. But I think history has proven that over the long term that's a very foolish assumption to make.
The end result is private entities taking money out of the system at some stage, and it doesn't shield you in any way from government incompetence or malice.
An example of one that doesn't would be a global decentralized protocol for transferring money. You're standing in a coffee shop in LA and want to pay for a coffee so you tell your bank to transfer $5 to their bank. It works the same if your bank is in Brazil and their bank is in Switzerland as if both banks are in Nebraska, involves no intermediary other than each party's bank, and their bank shows them the transfer immediately so they know to give you the coffee.
Then the panzers roll into Washington and der Führer wants to reintroduce financial surveillance to make sure nobody is covertly buying a computer that doesn't censor the internet. Obviously they can force the bank in Nebraska to inform on the dissidents, but your bank is in Brazil and the seller's bank is in Switzerland.
Unless the system allowing that is dismantled ahead of time so the dystopia can be switched on overnight instead of needing years to erode entrenched decentralized infrastructure.
This is to say: All currency is about control and convenience (you trade "invisible transaction" for "easily able to resolve payment") because those in power want to know/control the money and everyone else wants convenience.
Right! Like all the other monopolies that governments already have: public security (police and courts of law), external security (armed forces), public healthcare in many civilized countries, inspection of health regulations and consumer safety, monetary policy, etc.
> you trust your government not to ever be incompetent
Oh, I don't. But Apple, Visa, Mastercard and Google Pay aren't very "competent" either.
> history has proven that over the long term
History has proven that privatization of many of government monopolies are disastrous: Roman generals making private armies and destroying the Republic, abuse of forced labor from inmates in private prisons, exorbitant fees from payment providers (Visa, Mastercard), food dangerous for public consumption because the governments didn't inspect them, etc.
Your examples are things that aren't inherently monopolies and are significantly worse if you try to make them such. It's better to give people the right to self-defense than to put them in jail for violating a "public security" monopoly for not allowing someone else to kill them when there were no police around. It's cruel to prohibit someone from paying for their own healthcare in cases when the procedure exists but the public system won't spend the money. What argument could you even make for prohibiting private inspections of products and services the likes of Consumer Reports?
The things that are better as a monopoly are so rare that they plausibly don't exist.
The article doesn't say and I know nothing about India. I could guess consumers are oaying using their smartphones. So Google/Apple duopoly are still the gatekeepers to use UPI making huge profits. Of course using one of the American backends would make their control and profits orders of magnitudes bigger.