I'd love to see a prosecutor in cases like this respond to such idiocy by agreeing with the forensic psychologist.
"You're absolutely right, sir -- the defendant has plenty of things in his past that drove him to do these horrible things. All the more reason why the bastard needs to be executed as soon as possible!"
I agree with you. The compassionate thing to do is to put them in a state that relieves them of these memories - the state of death.