I'm an Attorney in America, and I can tell you with confidence that in no jurisdiction is a medical diagnosis of mental illness enough to complete a defense of insanity.
Is the medical profession somehow obliged to adopt the definition of "insanity" the legal profession uses? Or, perhaps I should ask is the legal profession obliged to adopt the same definition of insanity the medical profession uses?
I thought to be legally "insane" the ... "defendant" must not understand the quality and or nature of his actions. In other words, if someone thinks he's picking daffodils when, in reality, he's stabbing his aunt Martha to death with a kitchen knife, he's insane.
The medical profession tends to use more case specific terminology ... I don't think, unless I am mistaken, that "insane" is actually even a legitimate medical diagnosis. Sorta like the word "crazy."
Perhaps the reason why "insanity" is unpopular is that it so rarely works. Just because one might be "mentally ill" doesn't mean he doesn't know the difference between picking daffodils and stabbing relatives to death.