One of the main selling points of cryptocurrencies is decentralization, of not needing to trust a central party in order to use the currency. But the cryptocurrency doesn't actually eliminate that trust, it simply moves it. It moves it into trusting the protocol design, trusting the implementation of the clients, trusting your local hardware and OS to not be compromised, and in the case of smart contracts, trusting the smart contract to not be buggy. What's worse is in the centralized case, as long as the government continues to function you have lots of options for what to do if a transaction goes badly. In the cryptocurrency case, for the most part you're SOL, because cryptocurrencies by design don't allow anyone to e.g. void a transaction.