Well, i already have my reservations when it comes to regulating Cryptocurrency. From my interaction with friends, it's seems regulating the activities in the cryptospace will facilitate mass adoption of Crypto currencies and reduce the rate at which projects rug pulls. But then, if we accept crypto regulations, what happens to the decentralized feature of crytocurrency/blockchain?
This may not really give a big influence on the centralized currency. However, not all countries will accept this easily, the regulation of crypto is very complex and difficult to control. Although there are some easier regulations that make crypto accepted, in fact, there may be some regulations that are working on this regulation seriously.
Btw, each country has different regulations. We can see some positive and negative sides about the regulation, moreover related to the taxes. However, I don't think that this crypto will disturb fiat or centralized currency in the country, because they are fixed and centralized. Related to the decentralized features of the cryptocurrency, there must be some ways change if crypto is fixed regulated by the government. But the question is, can they exactly? They may regulate some terms like the exchanges and other platforms, or the project developers or companies, but in fact, there must be complicated to regulate the decentralization.