The Insanity Defense

Ken and John debate (use?) the insanity defense. What difference does it make if the person who commits a crime is, in one way or another, mentally ill? Does this make punishment illegitimate? Why is punishment, rather than therapy, ever legitimate? Which sorts of mental illness should exempt a criminal from punishment? Inability to know right from wrong? Inability to resist compulsion? Irrational depravity? John and Ken defend themselves with Susan Wolf from UNC Chapel Hill.