I think cryptocurrencies are not able to defeat fiat currencies without changing nations culture and ethics! what do you think?
that is absolutely true, without government assistance it is impossible for FIAT to be replaced. and it is also impossible for the government to want its currency to be replaced by bitcoin. This is very unprofitable from the government side. even though bitcoin was finally legalized, the government would still prioritize their currency. this aims to keep Fiat first.
It can't replace fiat for now and it doesn't have to. Cryptocurrencies' function these days is already enough since it provides convenience and faster transaction and great investment but fiat has been the traditional currency and people are still in the process of adopting the latest technology. Crypto is just good enough to support fiat but it doesn't have to replace it.