There is a lot of stigma for mental illness, far more than for illnesses outside of the brain. But I get the impression that there are various reasons why mental illness isn’t going to be accepted the same way we accept physical illness anytime soon.
For one thing, accepting mental illness means accepting that dualism is a myth. The idea that our self aware consciousness is not some ethereal thing separate from our brain, but intertwined with it on the deepest level is hard for people to deal with. The fact that a TBI or mental illness can turn a happy and social person into someone who is mean and depressed is scary to a lot of people because it shows our consciousness isn’t something separate from our brains. A person can be a devoted and loving parent, but then suffer a TBI or mental illness and become angry, apathetic and mean. I read a story years ago about a loving and devoted mother who survived a car wreck. She had a serious brain injury and lost interest in her kids. The doctor told her family to hold a mock funeral because the original her before the injury was dead now and wasn’t coming back, even though their mothers body was still there and she was still alive.
Or like how in psychosis or mania a person may become extremely religious. People hold religion sacred and accepting the fact that a biological illness can deeply affect your views on religion is unsettling to a lot of people. People have gone from secular, to deeply religious, to secular again before, during and after an episode of psychosis or mania.
But also some mental illnesses make you dangerous to others, especially the cluster B personality disorders like antisocial personality disorder (sociopathy), narcissistic personality disorder, borderline personality. The dark triad (sociopathy, narcissism and machiavellianism) is strongly tied to destructive behavior. I think some studies show that 2% of the general public have anti-social personality disorder, but 40%+ of people in prison for murder have anti-social personality disorder. My understanding is there there is a large overlap between people who have narcissistic and sociopathic traits (clinical and sub-clinical), and people who engage in sex crimes. Its harder to feel empathy when your mental illness makes you hurt other people.
Or hygiene. Various illnesses like psychosis or depression can make you lose interest in hygiene. That makes it harder to gain acceptance. Feeling a little sad is one thing. Feeling so sad you smell like body odor is something else for a lot of people.
I feel like brain illnesses affect us in ways that deeply affect a lot of unspoken assumptions we have, and addressing that means questioning those assumptions. I think that’s one reason recreational drugs are mostly illegal too, accepting that physical chemicals can affect our sentient consciousness is deeply uncomfortable for a lot of people. One recreational drug can make you feel intense love and compassion. A different recreational drug can make you feel intense rage and irritability. Thats distressing for people to accept.
But why do we put elderly people with brain illnesses like dementia in medical facilities, but young people with brain illnesses are left to rot in the streets? Neither consents to treatment because the parts of the brain that give you the ability to consent to treatment are affected. But for one we take that decision away and for the other group we do not.