of course bitcoin is used for illegal stuff, we cannot do anything about so i dont worry about it
I think we will not know the purpose of transactions of everyone in bitcoin. although the transaction id they can see but we will not know what they do with the transaction. so I think bitcoin is great to be used as payment for illegal goods. and I do not know if many people are using bitcoin to buy drugs and so on
Same goes up for fiat related transactions. Even if you use internet banking to send money, no one will be knowing what the purpose of that transaction was. And especially when it comes to cash money transactions. Bitcoin isn't any different. It's a currency that is being used for all kinds of purposes.