Seriously, by Mises on definition it's not FIAT. No government has deemed it legal tender and no one will. Why? Because no one has central authority over it.
Look if you are going to argue what is money then there is no question about it.. gold and silver is the best form of money. But I'm not talking about money, I'm talking about currency. Gold and Silver suck as currency. Hence the reason fractional reserve banking even came about. Until there is a virtual commodity back currency, the best alternative is one that mimics one.
My arguement is not Metals vs Bitcoins it's Dollars vs Bitcoins.
If you rather use dollars instead of bitcoins you are part of the problem.