Bitcoin will never replace fiat. It will always be just another option along with fiat.
Then how will it ever be truly useful, if its is always susceptible to rampant manipulation against fiat?
It has certain characteristics that make it useful that fiat can't do. Like sending to another country in a second. Just like a credit or debit card didn't replace fiat.
If Bitcoin remains an obscure vessel for only a select subset of transactions, then the game theory behind the network crumbles over time as difficulty increases and block reward drops
