Somehow they don't seem to be nearly as harmful as cigarettes. Remember he government propaganda from what was it the 80's? Where they claimed one joint was a destructive as a whole pack of cigarettes? Anybody who smoked both, which at the time included me, knew that to be total bull$#@! . Don't listen to that source anymore. Later they revised it to four cigs but it still wasn't true. If it had been it wouldn't of mattered. Funny thing about people is lie to them enough and they just quit believing you. In fact by far the most deaths associated with MJ come from prohibition and therefore turf wars over illegal sales territory.
However, I would never condone smoking anything. We have much better ways to ingest MJ now for those who wish. Because no smoke is harmless. Not even campfire smoke , which most people can literally feel the next AM