Well the same can be said for any thing. Even a car can destroy, a plane, a kitchen tool such as a knife, a set of stairs (someone can fall)... you would have to show me science that proves weed hurts the body. Also many people have severe pain from medical conditions and why should they live their life in pain when there is a remedy? Lastly not all pain is physical. Some people suffer emotional pain, and use it to relax. Adults have the free will to decide under a democracy to do what they feel is right for their own selves. I see no harm in that. Anything in moderation is ok in my opinion as long as it does not harm another human being.
There are studies that show that weed has an adverse affect on brain development up to the age of 25. I'm not sure how much has to be consumed to affect it though.
look at addicted people and then judge by yourself
and i agree with you @movievigilante