I don't think the state even needs to go that far. Just have a (gradually increasing) number of press conferences where serious-looking men in uniforms talk gr

I don't think the state even needs to go that far. Just have a (gradually increasing) number of press conferences where serious-looking men in uniforms talk gravely about the dangers of Bitcoin and how it is used by criminals to facilitate drugs/human-trafficking transactions. Then have a think-tank with a respectable-sounding name release a report saying that very few law-abiding people use Bitcoin and that there are $X billion of criminal transactions annually. Then a concerned politician can sponsor a bill that makes owning Bitcoins prima-facie evidence of criminal intent to sell drugs/contriband/whatever as part of his/her "tough on crime" initiative. This will result in a positive feedback loop: The utility of Bitcoins for "regular" people will fall and for "criminals" remain about the same, increasing the criminal fraction of the Bitcoin economy. It won't kill Bitcoin outright, but it will prevent Bitcoin from being anything more than a marginal player.