@AviK
Goodman is not the be all to end all in legal decisions. His explanations are nice for the layman, but not the rule of law/bar standards, etc. that vary by jurisdiction.
Your constant pursuit of this topic may be entertaining to you and a teaching opportunity for me, but are probably boring and off topic for most CR readers,
Please note: Mentally Defective does not equal criminally insane, and not everyone with a mental defect pleads an insanity defense. A potential 2-5 year sentence in prison, may be far more appealing than a possible lifetime in a mental institution.
Lawyers don’t have to believe in the case they are presenting, they are not paid to do so. It helps, but is not a requirement of doing one’s job.