I think that it's simpler: people have long been encouraged to believe that certain medical procedures and practices that lack great evidence are responsible for saving their lives, and that anyone who critiques those procedures in any way is trying to kill them. People who are paid (as often as not by government) to provide those procedures and practices encourage these beliefs, and spend massive amounts of money in lobbying through patients' rights groups and other channels to support and encourage people in that fear and anger.

People who are sick either continue to be sick, get well, or die. No matter what diagnosis or treatment you give to someone, they either get better, don't get better, or are removed from the conversation. We never hear from the dead again, the people who get better insist that you saved their lives, and the people who don't get better will be attacked by the people who did for not believing or trusting you enough.

That study does not support your intuitions on this matter, but merely excludes seratonin as the basis for a chemical imbalance causing depression. It does not show that there exists no material cause for depression, only that there is strong reason to believe it is not related to seratonin.

First of all, that study is about challenging a specific chemical imbalance, which was not that well supported anyway.

But I think mental illnesses challenge our very old notions of free will, willpower and control. How much are you really in control when the mental structure for motivation in the brain is broken? Personally, it's not like I pulled myself out of depression. I just took advantage of a "break" my brain gave me.