I don't think we can stop that. The transactions made in cryptocurrency are always Anonymous more than enough to be as useful as it is for the illegal transactions.
It is impossible to stop the use of cryptocurrency for illegal purposes just like stopping other crimes in the world. Moreover, cryptocurrency has a high degree of anonymity and can quickly move around the world, which makes it extremely difficult to combat abuse by law enforcement agencies.
Cryptocurrency is a relatively easy prey for hackers, scammers, and other attackers, so you should most likely expect an increase in crime with it, rather than a decrease.