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 is really dangerous because many people are being trick or scam from this fake bitcoin sites and maybe this is one of the reason why the government of aome coutries banned bitcoin because of this crimes. Like just you said they are untraceable so they cannot put to jail for the crimes that they had done.