We have laws about what you can say in real life. Fire in a crowed theater for example. Even if the things said are not in themselves illegal, if they cause someone to take an illegal action, or attempt to take action but fortunately caught in time - you can be held liable as partially at fault for the illegal action. It might be legal to plan a crime (different countries have different rules, but this is often done at parties where nobody is serious) but if you commit a crime or are serious about committing the crime that is illegal.
How are we going to hold AI liable for their part in causing a crime to be committed? If we cannot prevent AI from causing crime them AI must be illegal.