The problems with bitcoin, as seen by governments
1. You can't regulate it. You cannot block a bitcoin transaction. The only thing you can regulate are things like exchanges and the businesses accepting bitcoin. If more and more people start to use only bitcoin for their entire transaction and not exchanging their coins for fiat currency there will be less and less to regulate.
2. Financial institutions don't like it. The bitcoin network does not need them so in an all-virtual-currency world they would soon perish. Obviously, they are using their financial influence to lobby governments to do whatever they can to discourage the usage of these cryptocurrencies.
3. You can't seize bitcoin. You can't freeze their wallet. If they have bitcoins, they can continue to buy things. Freezing a bank account to dry up resources for people not behaving exactly like the puppets the government would like them to be gain greater freedom, which is of course unwanted.