I could understand you saying that if it was true, but sadly it isn't.
Cannabis and mental health
My wife works in mental health and sees youngsters that would have had productive lives suffering from psychotic illness from cannabis.
I think the reason you do not see it legalised is because it would not pass the strict compliance testing to put a drug on the market.
People do not really know the effects, they think nothing is happening to them because it is not a physical pain, but they may well be affected by it, and be completely unaware.
It is known that it is harmful to the brain, but how do you measure that harm? What is the acceptance criteria for mental impairment for a drug being released on the market?
It is a wolf in sheep's clothing. People assume it is safe, but do not see the real story. Psychosis from smoking cannabis is common. And puts a young brain, under 30 years of age, at considerable risk of impairment.
I am not for criminalising the young, but I am not for releasing cannabis into the community either. I am not sure what the answer is, but legalisation is not it.
It is a bit like the gun. Just because people want it, doesn't mean it is safe to give it to them.