Well, sometime back I asked one of my outreach workers (JX) "How come natural selection hasn't got rid of Schizophrenia?". She gave me various papers, one of which is called
Creativity, Evolution and Mental Illnesses. If I've read the paper correctly, it appears that schizophrenia contributes extra creativity to the general population. In other words, schizophrenia helps the group at the expense of the individual. I'd like to point out that, while meds are important, they do tend to inhibit thoought as opposed to promoting thought.