No matter how sad it sounds, bitcoin is still used for illegal activities, especially for the sale of drugs. For drug dealers, bitcoin is a gold mine. Imagine, complete anonymity, deaf the need for meet with customers, Ah and laundering money. How to deal with it? Nobody knows. But you need to fight.
Yes there are some sectors or sites that are using bitcoin in some illegal aspect such as gambling. Theyre using bitcoin as their bid and then they will use it to earn money easily. But the profit there is not sure because it is a 50/50 process. You cant predict if you will win you will lose.