I was reading about the two types on insanity pleas, known as 'NGRI' (Not Guilty by Reason of Insanity) and 'GBMI' (Guilty But Mentally Ill). For example, a good excerpt is here on Google Books.
However, something very obvious is bothering me:
How can you have a legal system where on one hand we consider insane people not guilty of their crimes and on the other say that they can be guilty? Isn't it a contradiction?
If insanity is a valid "excuse" to escape responsibility for a crime, then why isn't it always a valid excuse? Why would we allow insane people then to be found guilty? We already acknowledge in our legal system that insane people are not at fault.