"I cannot see why people are having their life’s ruined for smoking a plant that is in my opinion safer than both cigarettes and alcohol' bit."
It's perhaps b/c with Marijuana, the effect is stronger than with cigarettes or alcohol? I honestly have no idea but I guess a person can drink one or two drinks and be okay, if a person smoked marijuana, he/she would feel the effects right away? and cigarettes too, a person's mental state doesn't change as quickly.
I'm not 100% knowledgeable with this things since I don't smoke but my mother does.
Just wanted to say that, not truly an opinion, just giving a reason to why some people wouldn't allow it.