A far better approach I think is a ballad for the loss of a loved one due to smoking, One can never underestimate the power of music to change lives, as one struggling right now to stop it is something that I am trying to keep in my mind.   

There is nothing funny about generalization of people. Even if the intent is at humor it will get lost and regarded as hate peddling which I do not believe was the intent of your song ... rather than use terms as Scum maybe a ballad of those lost to the habit would hit the heart more I think ... just a humble suggestion ... In that light I will wish you success in your song writing. It is always nice to see people writing their own music.