Maybe I'm reading too much in to your comment, but with cigarette smoking there is a lot of the "if you want to destroy your lungs" attitude that I hypothesize stems from the puritain "if you want to prioritize enjoying something over long term health, I'll be especially harsh towards you". I 100% understand the infringement (or at least encroachment) on your right to enjoy the outdoors and believe it is very rude to expose someone to obnoxious smoke. But judging the "destroying your lungs" aspect is nobody's business but the person doing it. You may not have meant it this way, but I have seen a lot of people who do.
Edit - also, marijuana smoke is hazardous, just like tobacco smoke. Why would it be more benign?