Dude a tax isn't going to help a government to control and regulate digital cash. Hello, have you ever hear of tax evasion and talking specifically about the decentralized money, how it(s going to happen. Unless you use it with the bank account you own.
It doesn't help a lot but it will help the government to earn some extra cash and I hope it won't end up entering their own pockets.
That tax evasion thing is kinda impossible for Crypto Currency users even if they implement KYC(Know your customer) on every Crypto users on their respective countries, I heard and read some article about the Japanese government implementing taxes on Crypto users but it didn't explain how that law works on every citizen of their country that uses Crypto Currencies.
digital money does use the blockchain, known as decentralization, but I doubt ... is all blockchain-based currencies included in the decentralized category (I doubt this point)
for example, XRP, which can be said as a centralized currency because it gets support from the government and banks
I don't know much about XRP(Ripple) but I see some posts in this forum that it will be used by banks in the middle east. I think this is one of the reasons why Ripple reached the top 3 on Coin market capitalization.
I immediately googled about the decentralized and centralized issue about ripple and I think its just FUD according to this article that I have read below.
https://coingape.com/ripple-clears-about-centralized-or-decentralized/