I wish BTC is not used for illegal activities though it is a currency. Legal and illegal activities require money. It depends on who uses the coins. Lets utilize the bitcoins only for good purposes as it was created to benefit all and lets bring more fame and name to bitcoins and its founders.
With the anonymous factor and descentralized factor? I believe bitcoin was created for ilegal propouses or at least a lot of transactions are linked with something ilegal, we can't stop it and that's why bitcoin have this price.
I think we can not fault it, bitcoin has decentralized and anonymous is because someone(creator) wants a freedom and secrecy so that's why bitcoin made #imo. regardless of the user to use it for illegal activity or not, I think we have no right to interfere with it, because every user is free stree right ?