It's a transfer of value. Of cours it is used for illegal activities.
Not that its negative, it may be positive, because it brings a lot more of users and activity. Then again, it creates a bad image, so I am not totally sure..
Each and every day a huge transaction is taking place through bitcoin for illegal activities.
These doesn't mean bitcoin support it, but the technology gives a way that's it.
Well, bitcoin transactions are very difficult to trace, so very many people who take advantage of this moment to perform illegal transactions which can not even be on track