Good post. Especially last paragraph.
Address to you and Nelson:
First, in order to qualify as mentally ill at the time of the crime, the patient has to not be able to distinguish between right and wrong, fantasy vs reality. Obviously, most know this.
The defense of mentally ill is based on the "The McNaughton rule."
The first famous legal test for insanity came in 1843, in the McNaughton case. Englishman Daniel McNaughton shot and killed the secretary of the British Prime Minister, believing that the Prime Minister was conspiring against him. The court acquitted McNaughton "by reason of insanity," and he was placed in a mental institution for the rest of his life. However, the case caused a public uproar, and Queen Victoria ordered the court to develop a stricter test for insanity. There are definite cases where the McNaughton rule applies (e.g., in the case of severe paranoid schizophrenia--the patient believes people are conspiring against him or her).
Again, the media throws around the word "mental illness," but they never really define what it means. Typical media doing what it does best: providing false information.