It is not as simple as "The government likes to control and tax the movement of money" that makes them seem evil or greedy. The truth however is that if all currencies are decentralized, who would determines their value?
Bitcoin is only in the virtual form, how can we protect oourself from hackers or technical glitches? These questions are just some of the reasons why there is no telling what the future of cryptocurrencies holds, but it isn't wrong to say that Bitcoin and other cryptocurrencies will not be replacing government-backed fiat currencies any time soon. This however does not mean that there isn't a future where cryptocurrencies will be treated as regulated global currencies. Of course if we include the corrupt institutions, politicians then we can say the government is evil and greedy.
For bitcoin to become truly succesful it must be both a medium of exchange and a reasonably stable store of value.
You are right.
Change in value of the local currency has happened many times in developing countries and has affected their economic. But developed countries usually are able to control the value of their currency. Assume that the fiat is replaced by a currency which is out of their control. It's normal that they don't want it.