“The prohibition against killing persons is the limit situation in ethics… If we violate this principle, we violate the moral order and the claims that personal reality make on us. This is not to say that torture, brainwashing, and slavery are less evil. It is to say that such cruelty partakes in the fundamental depersonalization of which intentional killing is the prime, irreversible example. An ethics of radical personalism yields to the exceptionless moral principle that personal life must not be negated — because in doing so, the foundation of moral experience itself is rejected.”
(John Kavanaugh, SJ, Who Count As Persons?: Human Identity and the Ethics of Killing, p. 120)