We'll need to spend more in mental health just from legalizing marijuana.  Just as legalizing gambling preyed on the weak and poor, this will do the same.  Poisoning our citizens and youth in the name of the almighty tax dollar.  

From the Harvard Medical Journal: 
While cannabis may have an effect on the age of onset of schizophrenia it is unlikely to be the cause of illness,” said the researchers, who were led by Ashley C. Proal from Harvard Medical School.

“In general, we found a tendency for depression and bipolar disorder to be increased in the relatives of cannabis users in both the patient and control samples. This might suggest that cannabis users are more prone to affective disorders than their non-using samples or vice versa.” Future research is needed to understand this relationship.