If a currency can be used completely free of interference from the government, then it can and will be used for crime. In fact, if crime is easier and more profitable because the finances are safe and protected, there will be more of it. Eventually victims of all this crime will demand, rightly, that the government put a stop to it. So in come measures where government can interfere in the finances of the currency, for the purpose of preventing crime.
The power is zero-sum and it'll always be a trade-off between who has it. Total government control has problems because of potential abuses, by politicians. But a complete lack of government control also has problems of abuses, for crime. Both are bad, so it'll always be a trade-off.