There is definitely some harm from inhaling smoke from burning anything, but I wish there were more studies on how human lungs are more capable at dealing with smoke than any other species. It's not to diminish the harm but humans literally evolved around fires. Controlling fire was one of the first technologies ever, and I bet since then people have been smoking plants for all kinds of reasons. Only recently has chemistry allowed for unnatural substances to be made which even a pinch of it can kill you. My personal experience is that smoking plants isn't that addictive overall (you have to try to abuse it), and the main problem is second hand smoke.