At what point do you consider mental illness as a blame for murder/rape?

To me, mental illness is never a choice. Mental illness as the cause for being a serial killer, child molester, rapist, whatever it may be, is not a choice. I’ve been hearing some people claim that someone can choose to be a pedophile (not child molester——there is a difference: one is an attraction, one is an action) and a serial killer. You can choose to molest children and you can choose to kill a bunch of people, but how can you choose to have urges to do those things? Things can go wrong in the brain without choices being made; the brain is extremely powerful and if something is wired the wrong way, it may cause you to become a serial killer or a rapist or something like that. You might as well say that people choose to be depressed.

I believe that someone who is wired “normally” will not kill a person. They may have an urge to, but they won’t do it. This is where I draw the line at mental illness being blameworthy. That doesn’t mean that I think all murderers should get the insanity plea—that depends on the degree of mental illness and how self-aware someone is. But I do think that a bit of mental illness plays a factor in all murders.

This question is kind of asking a second thing in the first paragraph. Feel free to address both things it’s asking. I could only fit one in the “Question” spot.