You can't legalize marijuana while education is subpar. It has to be done the opposite way. Also, why to legalize something that is harmful to your body and brain [1]? I mean, there are SO many publications about it.
Easy to justify that one: the amount of deaths prevented from gang crime attributable to cannabis trade would far outstrip any potential harm caused by legalisation.
Besides, that's not a good way to look at it. The better question is why criminalise an activity that does no harm to others?
[1] https://jamanetwork.com/journals/jamapsychiatry/article-abst...