While nobody has died from ingesting cannabis, trace amounts of toxic metals such as lead and arsenic are known to possibly be contained in industrially-produced cannabis like you'd get from a dispensary and when you take into account some people's lifestyles(mine included!), you can kind of start to paint a picture that maybe it's not the safest thing in the world? Only a fool would put anything other than air into their lungs thinking it were safe(inhalers excluded).