Monsters, among other brutes, are the ones without guilt feelings. Perhaps Hitler did not have any, or Himmler, or Stalin. Maybe Mafia bosses do not have any guilt feelings either, or maybe their remains are just well hidden in the cellar. Even aborted guilt feelings...All men need guilt feelings.
On conscience: two essays (ed. Natl Catholic Bioethics Center, 2006) - ISBN: 9780935372489