I have gradually come round to the idea it should be legalised, and taxed/sold in the same way that tobacco and alcohol are. Until about 10 years ago, this wouldn't have been my point of view.
I agree with the points made by others,that cannabis seems to be very dangerous for some people, but much less so for others. A couple of my daughter's pals (lively boys) ended up on the psychiatric ward after smoking themselves into psychotic states when at 6th form. One of them is now fine, runs a business, happy young man in his late 20's. The other young man hasn't recovered his mental health.
Friends with MS and chronic pain swear by it - and given the addictive nature of pain killers as discussed on another thread, it seems unfair to dismiss it out of hand, and criminalise otherwise law abiding folks who do nor harm to others, and contribute to society etc. Someone I know of was prosecuted for growing, but the case wasn't proved at a jury trial. He was a former para trouper, who had raised money running marathons, and done his knees in. He had an expert witness who claimed his use of cannabis was of more use,and less dangerous to him, than the amount of pain killers/other medication he'd have need otherwise.