>We have evidence suggesting that cannabis use, primarily THC in cannabis, in genetically predisposed or at-risk populations, leads to earlier diagnosis of psychosis/schizophrenia. This tells us that THC in cannabis has a small causative effect on schizophrenia.
A small effect on people who were already at risk. The sky is hardly falling with legalization.
Emphasis mine. This seems interesting to me. Earlier diagnosis is not more diagnosis. It could just mean that due to illegality, these people got into contact with mental health professionals earlier than they would have otherwise. Also getting the diagnosis earlier. But not being more schizophrenic.
I'm generally pro-legalization, but if marijuana is shown to make people schizophrenic who would otherwise not become schizophrenic, it's a big deal. It has severely affected their lives and those around them. Tobacco doesn't give everyone lung cancer after all, some are more at-risk than others. Quantitatively determining that risk, doing cost-benefit, etc, is important, but I don't think this should be dismissed out of hand as immaterial.
A small effect on people who were already at risk. The sky is hardly falling with legalization.