Long term usage of darn near anything will kill you. Eventually, all the steak that I eat will give me a heart attack!
The problem with weed is (like alcohol) it's mind altering. Cigarettes don't provide that sort of reaction. This isn't a debate between cigarettes and pot, but cigarettes don't provide the reaction that pot does. Now, I would agree that long term usage of cigarettes are more probably more harmful than pot...though I don't know that for sure.