James Gilligan published a book 13 years ago called "Violence: Reflections on a National Epidemic," in which he diagnosed the root cause of violence as deep shame and humiliation, a desperate need for respect and status (and, fundamentally love and care) so intense that only killing (oneself and/or others) could ease the pain -- or, rather, the lack of feeling. When a person becomes so ashamed of his needs (and of being ashamed), Gilligan writes, and when he sees no nonviolent solutions, and when he lacks the ability to feel love or guilt or fear, the result can be violence.
The choice to engage in violence is not a rational one, and often involves magical thinking, as Gilligan explains by analyzing the meaning of crimes in which murderers have mutilated their victims' bodies or their own.