Bitcoin doesn't have to replace the fiat currencies but it will because fiat currencies aren't stable to support themselves.
They are likely stable and that is why fiat currency is widely used in the the global economy.
As the Feds continue to print USD like there is no tomorrow their fiat currency has become very unstable, other countries have done the same thing and the writing is already on the wall. When the world market collapses (it could be as soon as April 2014) what other currency are they going to use? Likely they will want to use something that everyone uses around the world. It could be bitcoin or it could be some other crypto like currency they invent (so they can control it).
"Something that everyone uses around the world" = fiat currency
BittBurger today almost every normal person dream to see bitcoin as the globally acceptable currency while fiat currency shall crash soon due to manipulation of it by central banks. I hope we shall be able to use bitcoins everywhere in entire world and no ore fiat currency in our wallets
In case you are not aware, inflation of prices in a capitalist economy are avoided due the manipulation of interest rate by the central banks. So you entire premise is based on a wrong understanding of how fiat currencies are issued and for what purpose they are issued.