My ideas:

"Mental illness" is caused by thought censorship, not by "chemical imbalances in the brain". Chemical imbalances or something along those lines may arise and get established and maintained because of the original and continuing suppression of thoughts and feelings, which are themselves natural and completely without "value". "Value" is only assigned later by society, parents, whatever (and gets internalized). In this and other ways the system can get overwhelmed by contradictory demands. However else does one understand how obsessive-compulsive disorders get established, or manic-depressive instability develops, or "borderline personality disorders" or the confusion of thought in "schizophrenia" or the separation into alters? How does the split between "good" parts and "bad" parts of a person get started? Originally they are just parts, and get separated if and only if approval/disapproval gets assigned (internally) to them. Healthy outcomes arise only if there is a "constructive" management of the "parts" which conflict with the demands of living with other people, a management which allows the feelings or the parts to remain conscious even when their expression has to be modulated.

As for medications, I think I can see how they could be useful adjuncts to a real therapy, but not replacements for it, as seems often to be implied by drug company promotions, and accepted as such by many practitioners.

These are my present conclusions, FWIW.