Sure drugs cause crime, like forks cause obesity
This handout points out that just as the inanimate fork merely sits on the table, so do drugs. It can also help you point out, to your subject, that in-and-of-themselves drugs do not cause violence, the black market does.
The overwhelming majority of drug users do not want to hurt other people. And their use does not inspire violence.
It's Prohibition and subsequent underground market and corruption which is at the root of the violence.