Enforcing a specific payment method for fiat isn't the same as enforcing an actual currency though, and governments force merchants to accept *insert fiat of choice* all the time.
Care to name one government that has forced all merchants in the country to accept debit/credit cards?
Would love to hear some examples of some others about different methods that have become mandatory and every merchant in the country has to offer as an alternative and is forced to accept no matter the amount.
Merchants would be free to immediately convert their bitcoin to fiat, if that's what they choose to do. But if an individual wants to pay in bitcoin, then equally I think that they should be free to do so.
So merchants are free to....accept what others want, a rather twisted view of freedom of choice I would say.