Because of the semi-anonymous nature of Bitcoin, its used in ransomware attacks. Hackers breach networks and hold them hostage until payment is made to them. Hospitals and schools have been victims of these types of attacks. However, unlike cash, which was favored by thieves in the past, Bitcoin always leaves a trail in the blockchain that investigators can follow.
This one of the reason why government are afraid of bitcoin. This is also why some of the government ban bitcoin in their country. Use bitcoin in illegal transaction like that. But we can prevent this by making standard rules and regulations that abusive people can't abuse it.