Lets assume that starting in USA all bitcoin to fiat exchanges are banned.
why should we assume that? and why USA? the world doesn't start and end in USA, there are lots of other countries most of which are more interested in bitcoin than USA...
I believe ~ most people are attracted to Bitcoins because of its fiat value (or USD value). Deep under I believe that people are really not interested in the use of bitcoins in a decentralized platform/application
most people are interested in both. it is like an incentive. you get to use
a decentralized currency while gaining profit because of its increasing adoption hence rising price.
the number of people who only care about the fiat value of bitcoin and nothing else is not that many, it is usually newbies with little money invested in bitcoin wanting to become rich over night.
not to mention a lot of millionaires who are interested in bitcoin Because it is decentralized and nobody can control it so they want to park their money in bitcoin.