Well, it is not the problem with Bitcoin but the human involved. There are also cases whereby people buy and sell drugs or involve in any illegal activities using fiat.
Correct, bitcoin is a blessings why their are many people use bitcoin in a very dirty play such as what you have said buying drugs in which belongs to illegal activity. I am so curious why they want that kind of black job. Bitcoin supposed to use in daily which can be lead into the right path and can straighten a life of human being.