In fact, buying drugs with bitcoin has occurred a lot, especially in the darkweb. well, that's because they use bitcoin in a bad way, and it's been used since bitcoin has a price. maybe it happened till now.
It is such bad thing to do really and I'm not sure if this should be legalised in anyway. I'm not fond of dark websites and will never be because they just devalue the currency which we are using for the use of buying products and services sold like that way.
Yes, there are many more sites which sell drugs really and I have read on the forum only. But it's better to keep the distance and let not bitcoin spoil in that way. But the thing is will people really stop doing that and will they allow bitcoin to save its ass from getting banned.
Just imagine if websites like dark web got big share of bitcoin and if someday they get caught then Feds could just get the bitcoins and cease them forever. There will be major drop in prices and it will halt the bitcoin growth.