I think it's the THC that's the culprit in doing most of the harm. CBD seems to be more beneficial.
My issue with cannabis is that I don't really like people telling others what they can or can't do. I understand the impact on society, etc but I guess that's the consequence of living in a free society. I don't use cannabis because I find it boring but people should be responsible for making their own decisions and live with the aftermath for better or worse.
I also don't like the idea of someone telling me what I can or can't grow. These things are plants. It's ridiculous for the government to regulate them. Psychoactive plants are all around us, including many in the supermarket. People just don't realize this. Even things like opium, from poppy, grow everywhere throughout the US. It's also easy to raise in your own garden, as are cannabis and psilocybin. It's not even difficult to extract the morphine and codeine alkaloids from the residue on poppy seeds in the supermarket.
Coca, tobacco, peyote, psilocybin, opium, etc have been around forever and have been used responsibly by many cultures. It's not my fault western culture decided to isolate certain components and strengthen and abuse them. Same issue with sugar. Most sugar is extracted from beets. Isolate the simple carb and do away with the healthy parts. That's probably the worst drug out there causing the most morbidity.
You can't do away with illicit drugs. They're here and they aren't going anywhere and people are going to continue to use and abuse them no matter what laws are passed.
I don't doubt that negative consequences will increase in the early stages of the legalization of cannabis as use will increase. But, I predict that once it's no longer cool or a big deal to use anymore the usage rates will decrease.