Is it?
All the people I know that smoke don't grow their own, I would say he was a good candidate to start selling if he has already taken the next step of growing. Of course all drug dealers never started with soft drugs....
In balance I think it's fair to say that most people that smoke don't automatically progress to harder drugs either.
Speeding, light drugs and the like are fairly tolerable though, I still think it's acceptable to inform on more serious criminals, we all hate to hear of someones bike being nicked or vulnerable people assaulted etc.