I don't know of many people, if any, who deny the reality of mental illness.
The controversy is with how the justice system treats criminals who plead insanity, mental defect, etc.
Murderers like this one evade justice too often with a finding of "innocent due to insanity", or a similar worded finding.
The finding should be "guilty due to insanity" and the normal sentence for the crime carried out.
I agree.
Some states it is “guilty but insane”. Of course the punchline to the whole thing is that whether the insane verdict include the word guilty or innocent doesn’t change what happens to the person, they still go in the nuthouse usually for longer than a “standard” 20 to life verdict will put you in jail. Read an article in the 80s from a criminal defender about how defense attorneys were doing their clients a disservice by using the insanity plea because it usually resulted in longer incarceration, but because it included the word “innocent” the attorneys consider it a win.