Well, the hard truth is that every currency is used for illegal activities, and bitcoin is one of them.
In the dark web there's a lot of illegal things you can buy with bitcoins.
Fact is that all kinds of currencies and precious metals are being used to finance illegal activities, but still the media and average joe is blaming Bitcoin for this. They somehow don't realize that Bitcoin is nothing different than fiat. It's money. In that regard it shouldn't be weird to see that people use Bitcoin for all kinds of illegal things. Especially when you consider how convenient using Bitcoin is.