The American Psychiatric Association's Diagnostic Manual considers suicidal behaviour as an appropriate problem for psychiatric attention, but not homicidal behaviour. There is no scientific basis for this distinction. It is clearly a moral distinction, in which for purely arbitrary and irrational reasons homicide is defined as a moral evil that deserves punishment, unlike suicide, which is considered (appropriately) as a symptom of illness that deserves treatment. And yet moral value judgements are clearly not scientifically testable hypotheses, unlike medical diagnoses and treatments. The distinction here is between moral philosophy and medical science. The fatal flaw with moral value judgements is that they are of no help to us if our goal is to learn what causes violence, and how we can prevent it, which is where forensic psychotherapy comes in.