Fiat currencies definitely aren't necessary, there is an increasing trend towards digitization of currency, and blockchain based currencies are just the next generation of this. The problem is that Bitcoin came out, and everybody treated it as the successor to fiat currency, rather than an incremental improvement on digital currencies such as Paypal and Skrill. I think that if Bitcoin was never invented, but somebody like Paypal had implemented a blockchain technology first, then we wouldn't be in the rivalry scenario that we're in now.
Those who believe that the existing conventional currencies of states are not needed with the advent of crypto currency, apparently. absolutely not oriented in the basics of the economy. The economy of the state and its national money are inextricably linked. National money can not simply be abolished and switched to the use of money, which will not reflect the state of the economy of this country. This is absurd.