Bitcoins are not a currency.
It doesn't matter what YOU think. Even if bitcoin isn't official currency that approved by gov, PEOPLE choose to use it because they find it more convenient to use than credit cards. That's the power of markets. That's the power of competing currencies.
Who gives a shit what gov says, they don't have power over you or me. They are illusion, to claim you as a part of their slavery.
Varys: Power is a curious thing, my lord. Are you fond of riddles?
Tyrion Lannister: Why, am I about to hear one?
Varys: Three great men sit in a room; a king, a priest and a rich man. Between them stands a common sellsword. Each great man bids the sellsword kill the other two. Who lives, who dies?
Tyrion Lannister: Depends on the sellsword.
Varys: Does it? He has neither crown, nor gold, nor the favour of the gods.
Tyrion Lannister: He has a sword, the power of life and death.
Varys: But if it's swordsmen who rule, why do we pretend kings hold all the power? When Ned Stark lost his head, who was truly responsible? Joffrey? The executioner? Or something else?
Tyrion Lannister: I've decided I don't like riddles.
Varys: Power resides where men believe it resides. It's a trick, a shadow on the wall, and a very small man can cast a very large shadow.