Governments have fears in bitcoin because they cannot control any transaction related on it. See, that bitcoin is decentralized and no one can manipulate transaction within. Meaning once bitcoin operate in one country or government the income from any transaction within has no any return to government. The fears of government in bitcoin tax free because any transaction in digital form within is untaxable and government cannot control it. Also the possibility the used of real money will circulated in one state once bitcoin is fully implemented in one government, that's why government are not favorable in bitcoin used.
Government can't control transactions of cryptocurrencies but they monitor the money turnover, phone calls, sites you visit, amount of electricity you use every month etc. It was a shock when on the third day after we bought and plumbed in two miners, we received sms from one of the national banks: "We want to buy your BTC"!