Why is it illegal in the first place, you might want to ask your friends. If they say it's because people will get high and crash their cars, then make the obvious response... make it illegal to DRIVE while intoxicated.

If they say it's because people will get high and hurt others... make the obvious response... make it illegal to HURT OTHER PEOPLE.

Just making the "state of mind" illegal is jumping the gun, comparable to making it illegal to wear boots, because you might kick someone.