probably one of the dangers of cryptocurrency is when people need it more than fiat. when it happens, it is likely the country's economic system will be disrupted, since most of the state revenues are also derived from taxes on fiat. when people prefer to use cryptocurrency, then fiat will not have a price.
but do no think that there will be any wrong effect on the economy of any county if people accept bitcoin.
At first, I think there will be some political and social instability, as some people will be influenced by governments to fight the expansion of Bitcoin, especially those who do not understand the currency. However, for people it is easier to get information these days, and it would only be a matter of time for such individuals to realize that Bitcoin is not the problem, but the solution.