It's been proven that marijuana is not physically addictive. You can easily find information about that, and the differences between physical and psychological addiction through your favorite search engine.
My point was that the active drug in alcohol can kill you if use too much of it at once. You can't do that with marijuana.
Marijuana does not have to be smoked. You can vaporize it, which has no smoke/toxins and gets you high just the same. You can bake it into cake and eat it. There are all kinds of ways to get stoned without smoking it.
In fact, it turns out that smoking marijuana is less dangerous for your lungs than everyone thought. There was a recent study (this year recent) done by UCLA that found no link between smoking marijuana and lung cancer, even when smoked heavily.