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.
People have choice. they can either use it in a legal way or illegal way. we cant stop them, they have their own will oh how to handle it.
but these might change the image of bitcoin. people may look at it negatively because they can see whats happening and whats really the purpose of bitcoin in this world. people might hesitate to have it. And as we all know if people holds money, they can use it whenever they want especially if has a high value and if they want to make it higher more by engaging in a legal way of having money