Yeah, but what if it was substituted with art, or something similar. It's possible to produce a society which values mentally ill people without necessarily coercing them.
What if they don't want to make art? Being mentally ill doesn't necessarily grant one creative insight. What if they exhibit antisocial or violent behavior?
You mean what if they don't fit into our status-quo middle class concept of society? Well then we ostracize them... and parade the ones of that do fit the fantastical ideal as unappreciated genius.