Go speak to your local doctor and tell me cannabis does no harm, many Doctors have told me there are an increasing number of people seeking help due to debilitating anxiety because of cannabis use, it's too strong these days, I'm not saying that cannabis actually gives you anxiety but I have no doubt in my mind that it can awaken it in individuals that have it laying dormant, if you have any bad mental health genes smoking this stuff is like smoking a time bomb.
Also another anecdotal point, you compare affluent successful people to poorer unsuccessful people, which group do you think will be smoking weed the most?, everyone that is successful in my family doesn't touch the stuff, you walk onto a affluent housing estate, ask these people if they smoke weed, you'll be hard pressed to find anyone, yet in all the poor areas that I lived in everyone and their dog smokes it that they defend it to hilt saying it helps them, well it certainly doesn't help them out of the gutter, that's for sure, cannabis is a magnet to impoverished areas and it stops many people from getting the real help they need , my friend straight out admits if the drug didn't exist he would be forced to get help.
And on the other hand I've heard Doctors say it's completely harmless. People definitely have contradicting views on it. I'm sorry that you know people that have said that it has "ruined their lives", drugs can ruin lives, and I'm a strong believer in helping abusers rather than throwing them in jail. But in my opinion, it's no worse than being an alcoholic.
They say "Everything in Moderation", and I believe that is the same for the likes of Alcohol and Cannabis.