Most of crime is still done via fiat money, and governments are the widest perpetrators of crimes against humanity with constant taxation for war. Bitcoin is what allows people to be free from having their money be used to harm others.
Criminals is using bitcoin if they have enough knowledge about it and they cannot use it in crimes if they don't know how to operate it. Unlike fiat currency, bitcoin is not easy to access and not known by all the people and you will be having a hard time to retrieve your bitcoin when a crime happens if your country is allowing you to use bitcoin but if your country allows you to use bitcoin, you can use it but always be careful because you cannot retrieve your money all the time because sometimes no one can do a solution for a problem that is not experienced by the others.