We pretty much have that with regards to marijuana. I'm not sure why it's treated so differently from tobacco. In both cases you are inhaling the smoke from burning leaves.
Because you can vaporize it, turn it into oil and again vaporize it, bake it into food and eat it, etc. too. Even if you do smoke, a regular marijuana smoker consumes a lot less tar than a regular tobacco smoker since they need less plant product to get the desired effects. Plus, nicotine promotes cancer growth (but does not directly cause it) while THC may mildly inhibit cancer growth
Tobacco is unusually nasty, just look at throat cancer from chewing tobacco. Incense, woodsmoke, and Pot do cause problems, but the risks are significantly lower.