A current or ex-pothead parent cannot tell his kids to abstain. He/she hasn’t the authority. But he/she can tell them it’s a complete no-go as a steady lifestyle component, and that it’s almost guaranteed that daily or frequent turning on results in a lack of drive, ambition and discipline to some extent. In this sense pot is almost a worse thing to get down with than booze because boozers, at least, tend to perform better professionally.