Government are really scary about bitcoin because they bypass government policy and also rule and regulation. The evasion of tax is another way bitcoin is not supported by any government.
I think they are scary because of they cannot get some benefits from the bitcoin and they cannot control bitcoin like what they do with their fiat. and to solve this, maybe they will make a regulation to control bitcoin and cryptocurrency so they can know who is the people which stay behind the crypto and they can see how big the crypto can grow. maybe the tax is a good choice for them to control bitcoin user and they can get some money from bitcoin user and it means more money for the economic country.
I must say that the banking system is scarier than that of the governments for now and that the governments are sensing this thing that the crypto currencies will lead the world in much better way and that the fame of the paper money is being greatly reduced with the introduction of the crypto currencies. The government has to take some positive step to declare these currencies as legal currencies.