This danger is nowhere near imminent. For all the crypto anarchist idealism surrounding bitcoin, it exists by piggy backing on gargantuan, pre-existing financial and industrial infrastructure. If there was an economic meltdown taking out all the banks, then your ISP would cease to operate. So would the power plants keeping your computer turned on, and the submarine cables that allow you to trade with the other side of the world and providing liquidity to the crypto market and making it useful.

In anything less extreme than this apocalyptic scenario, TPTB have the capability and every incentive to make sure that their position at the top of the food chain is not jeopardised, and a crypto currency that is either truly decentralised or not controlled by them would at some point, in theory.

The ECB are hardly enthusiastic about bitcoin either.

About the only regimes openly (or covertly) in support of it are those that would benefit from destabilisation of western financial systems, all the while making sure that they have the capability to kill it stone dead when they need to.

Governments could build firewalls to block the crypto traffic they don't approve of. I'm sure that somewhere in China, a big red button to do this has already been built. It will be pushed when their government thinks that ending the use of non-state controlled cryptocurrencies overnight (within their borders, anyway) is a net benefit for the regime. Other governments are quite capable of doing the same, although I more suspect it will be graduated response of legislation, technical and financial measures. The end result will be the same, any threat to the monopoly of fiat and centralised control will be neutralised. Enthusiasts will be allowed to keep playing with their toy money over Tor or whatever, the market cap of bitcoin will go back down to 2010 levels and it can go back to being used by crypto-anarchists, curious geeks and occasional weed purchases. blah blah the economy will soon run on bitcoin and governments would never dare to stop it otherwise society would collapse etc. No, it will never be allowed to get this big in the first place.