im not buying or using drugs but i just want to share my thought about this. anyway, some people may use bitcoin in buying drugs or any illegal activities. this is because using bitcoin as a payment will not require you to divulge your real identity. thats is why some prefer to use bitcoin in dealing with illegal acts.
As good and bad people are present in all societies, as both good and bad people currencies for their intention, so if they feel the need or they consider bitcoin as more convenient for them then will certainly use it, but there is no blame on bitcoin for that, as bitcoin is a currency like other currencies and can be use for both good and bad purpose by the people.