Yes, nowadays its being used in crime, they buy and sell online and pay by bitcoin. Because its untraceable. So police cant get clue to caught them. I think its dangerous.
It will be dangerous depending on the person who are using bitcoins. Bitcoin is a digital currency and it can be used on different payment method online depending on the store but some of the people are using it for drug laundering and any illegal activities, in this case government are worried about their country.