Banning in bitcoin's ecosystem is really nearly impossible. You are right with your point that bitcoin is an opensource platform and it is not made to be regulated and is the user's choice and risk to use it.

However, banning it with the part that stopping and not allowing people to accept it and use it as a payment method is the thing to consider. You may have a bunch of bitcoin. But what would be the sense of it if the government already issued a law for the people not to accept it and not to consider the value of it? The government has the power to stop people from using it and consider it as an illegal deed.