of course fiat is necessary. because fiat is more or less safer currency comparing with other alternative currencies such as crypto currencies. they are mostly backed by governments and also easy way to make payments.
as long as the country we live in is not subject to excessive inflation, fiat currency is indeed safer, but in trade between countries it is more profitable to use bitcoin, because we will not be affected by the difference in the value of our currency to the destination country, because each country has an eye value different money, very different from bitcoin wherever we trade between countries, the value of bitcoin in all countries remains the same, because bitcoin is not dependent on the value of the currency of any country.