The control governments want is much more related to TAXES. That is the point. When you deal with the country's official currency, you are generating income for the government: international or national transactions. Without these taxes the government can't survive as the well-doer, the benevolent charitable and then its mightiness is in risk! They want people depending on the government, and Bitcoin threats this relation between state and people.
It's actually not about taxes. Bitcoin can already be taxed since the existing system (that has been in place for decades) covers pretty much everything. It's just people who assume that they don't have to pay taxes because Bitcoin isn't legalized or regulated. It's false.
Also, crypto in its entirety is still a niche market, so what's the government exactly losing when you don't pay due taxes? If there was no crypto there would be no
extra tax income for them at all, so in all cases they should be happy that at least some (which will only increase) people pay tax over their gains and whatnot.
Bitcoin is a tool allowing you to store your wealth outside the traditional banking system where governments and corporations no longer can terrorize you. If the government controls your finances, it controls you. If the government can't control your finances, they can't do shit other than to change their attitude towards you in a positive manner, because you are the one in control now.
Bitcoin can be already be taxed, but it can be used without paying taxes too, it's possible and most people go through this way. On the currently time it's still a niche, as you say, but don't governments think on long term, on what Crypto-Currency can become? And for them it's better to be prepared since now for what is coming, as it's inevitable.
The finances control point is valid too. There are many decentralized investment options nowadays without frontiers thanks to Crypto-Currency, it removes the money from the banks hands, so they can no longer make an huge profit and give you a little percentage of the total profit. The relation between banks and governments is too strong, if you affect banks income the government will suffer.