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.