That's not really an argument, though. Cigarettes are only addictive because of the things that have been added to them. Tobacco is kinda lame on it's own, really.
The same thing could be done with weed (not saying I'd enjoy that, but it certainly could happen) and then sales would skyrocket.
Besides, even without additives, it's still not an argument. People don't drink even remotely as much as people smoke, yet sales are still perfectly fine. In fact, they're one of the few products that don't suffer during a bad economy.
If weed was legal, here's how I'd imagine the "addicted" smoker's routine would go:
* Wake up, smoke
* Eat breakfast
* Go to class/work
* Eat lunch, smoke
* More class/work
* Go home, smoke
* Eat dinner
* Smoke
I know quite a few smokers who do that every single day, and it's not even legal. It would only increase if it was legal.
Besides, who's to say a pack would include 20 joints in it? People are assuming too much, IMO.