I'd say this needlessly increases the scope of the discussion, which is not "anything that is harmful". If that's the measuring stick, you should also be willing to discuss the banning of several food items.

Smoking is a poor lifestyle choice. Deeply addictive with negative effects to your health in the long term, that much is clear.

Heroin and meth can destroy you in less than a year. Physically and economically. It will bankrupt you and turn you into a zombie, after which you will do anything at all for the next fix, crime included.

Smoking does none of these things. It doesn't even alter your state of mind nor do you get high. Smoking doesn't fuel violence in a way alcohol can, nor does it make you delirious in a way strong weed can.