Actually is very helpful once the small community economy ..
The reason the state forbids is to apply the principles of prudence, safeguarding business competition, risk control, and consumer protection.
I think any government of any country wants every thing under their control so, its obvious for the government has no control over a decentralized cryptocurrency. Regulating or monitoring all transactions is merely impossible; and they cant really shut it down because there is no central location to make that possible. Hence the best they could do is ban cryptocurrency and implement penalty for possible offenders.