This is something especially important considering we live in a world where nation-states are increasingly weak, politicians are either seen as incompetent at dealing with economic issue or just straight up overpowered by transnational entities while people are more and more nomad (not hesitating to just abandon their countries for another one when they are not satisfied instead of trying to enhance it). The problem with this trend is that currently moving your capital with you is hard (e-banking is a progress but it's still not enough for most people, especially the poorest).
Finally there is this economic warfare aspect, not all countries are like the USA where the currency is a tool for global hegemony and a fundamental pillar of the state, in fact with the EU we have strong countries which for the first time in history have willfully abandoned their monetary sovereignty (they still keep control but it's not one-sided). Best examples of this dynamic is Japan which has seen the yen bleed badly during the last decades and is the first big country to have a pro-cryptocurrency attitude.
No, it means trusting Bitcoin exchanges in addition to your bank, because at the end of the day you still need to at least get enough money to pay your taxes. So until you live under a government that recognizes Bitcoin as money, you still need to cash out at least sometimes. Even if you somehow have no taxes to pay, you still need to do business with people who do, and they are either going to demand the government's money or they are going to take the relative value of Bitcoin to that money into account when setting prices.
You seem to underestimate the power of governments, especially when it comes to money. Governments tend to enforce laws dealing with taxes and debts, and those are the laws that give fiat currency its value.
"Japan...is the first big country to have a pro-cryptocurrency attitude"
Ironically, Japan is also the source of the clearest example of the role of debt laws in determining the value of money:
https://qz.com/1003609/bitcoins-soaring-price-means-mt-gox-c...
TLDR: MtGox is paying its creditors in Yen, despite having lost their BTC, because of the debt laws in Japan.
But sure, the governments as today can easily cripple cryptocurrencies if they decide to and I'm not underestimating their power but as I said there is a competition between states, if my country adopts a hostile behavior toward cryptocurrencies then I'm pretty sure another country with a more lenient attitude will be happy to welcome my capital and workforce (not really a new concept, it was already like that with huguenots 400 years ago and it weakened badly the top dog that France while boosting immensely second or third ranked powers like England and Prussia).
I think the leaders in first world countries already understood that, that's why the general attitude is to say "it's none of our business" right now, especially in places like Europe or Japan which kind of missed the first wave of the "third industrial revolution" like internet is called by regulating too much or having a top-down approach to develop the sector and in result got crushed by the USA.
In short: ban cryptos at your own risk.