Being a teenager of the 70s, all the folk I knew that smoked weed were responsible hard working people who also trained/studied whenever necessary. There is much talk about it creating mental health problems but my only example of this was, 'people paranoid of getting caught with it' and I do recall one incident of a first time smoker who demanded to go to the local ED hospital, but we were able to reassure her to relax and just 'enjoy it' which she did. I wonder how many people when they have weed for the first time, do the exact same thing, resulting in avoidable admissions and askew statistics.
Also in my experience, people only used other drugs when weed was not accessible and personally I found these other drugs (chemically manufactured ones) to be hard on the body and therefore my use of them was short-lived. I think I can confidently say that after experimenting with many substances which included alcohol and cigarettes, that marijuana is the least problematic of them all. I believe the worst (legal) drug of choice is alcohol. It seems odd to me that people are able to drink to relax and unwind but they are not legally able to smoke marijuana? I believe all drugs should come as a health issue not a criminal one.
I do not believe there is a physical need to smoke marijuana and it can easily be stopped by working on 'the reasons why you do it'. Most people I know stopped smoking when their children came along and/or gave up whenever they wanted to.