Having smoked it daily for some 8 years, I feel a bit qualified to have an opinion. I see some dangers:
1. Lung cancer and brain cancer, perhaps even more dangerous than tobacco, and since you mix it with tobacco, you get them both. Drinking it as tea or baking them in cakes would minimize it and leave "only" the brain cancer.
2. It almost inevitably leads to the use of stronger drugs, because there is always ome dude in the gang who uses other stuff and you want to be as cool as he is and so on. Also, you have already crossed the line and the limitations for crossing new lines are smaller than it was the first time.
3. Using much of it, as I did, leads to your living a life rather void of social interaction with "normal" people, as you after a while almost only manage to interact with your likes, and you sort of strengthen the fringe behaviour, you become more and more set aside from the rest of the people. Interest in school, labour, other interests diminish, all your life circles around is da weed.
4. Long-term results. You kind of stop your mental development at the age when you use it - and this is rather seriously meant, intended, from my side; you see so many grown up previous weed-smokers in the 40s and 50s and 60s, dressing and behaving as if they were still 18. Now that of course can be a very good thing, keeping the youth in yourself alive, why should you grow old in your mind-set etc. - but is also can be a very pitiful and pathetic thing to observe, when at gigs etc. you see these old hippies who never grew adult-like, never grew up, but are stuck in their old notions. Apart from that, there are long-term results such as psychic problems, physical health problems, you react strangely to things, you can get flassh backs, you do not manage 100 % to interact with people, the years and your wife and your children and your closest ones never are 100 % close or real to you because YOUR MIND ALWAYS IS SOMEWHERE ELSE - and that is BAD. Good ole' Jim Morrisson in an interview once said that he felt "a gloomy pleasure", never was "quite happy, quite at home, quite there" - and that sums it up pretty well, I think.
Greetings form one who was there - and who sort of still is - if you got my last paragraph.
TOH