I've had the argument here more than once. What convinced me that there was more to mental illness than "just having a good attitude" was a childhood friend -- one of 5 children -- who contracted schizophrenia as a young adult. She turned from a smart, cheerful, outgoing Christian young woman to someone who talked to light bulbs. Along with that I've had a few friends who have gone through major depression for no reason and antidepressants made all the difference with them.