Legal matters are almost never black and white. If someone does something illegal using my service, and some other 3rd party sues me as party to that illegal behavior, from a legal perspective having a clause like "no criminal behavior allowed" in there makes it easier for your lawyers to argue "my client clearly didn't intend to authorize/facilitate such behavior". This argument is of course made much stronger if it is paired with behavior, like banning (or attempting to ban) the criminal user as soon as the activity was identified.

But if you are paranoid you should speak with a lawyer in your jurisdiction.