After Joe Horn killed two burglars, a grand jury no-billed him. Apparently this shooting was legal. But when something is legal, it does not necessarily follow that it is ethical or moral. How does the Horn shooting stack up against Catholic moral philosophy?
The Catechism of the Catholic Church conveniently includes an entire article on the fifth commandment ("You shall not kill") which explains exactly when one may morally kill another human being. Paragraph 2264 declares,
[I]t is legitimate to insist on respect for one's own right to life. Someone who defends his life is not guilty of murder even if he is forced to deal his aggressor a lethal blow.
In principle, then, Catholic teaching allows the killing of another human being for the purpose of defending one's own life. We are stewards of the life God gave us, and we have a duty to keep it safe.
The Catechism has more to say. Paragraph 2263 explains:
The legitimate defense of persons and societies is not an exception to the prohibition against the murder of the innocent that constitutes intentional killing. "The act of self-defense can have a double effect: the preservation of one's own life; and the killing of the aggressor. The one is intended, the other is not."
Double effect is a philosophical principle of Thomas Aquinas, the source of the quotation in the paragraph above. The rule of double effect can be contrasted against consequentialism, commonly stated as "the ends justify the means." The essential difference between the two is that according to consequentialism, intention does not matter, while according to the rule of double effect, intention is key.
When consequentialism is applied to this situation, Horn's actions appear to be proper. If the ends justify the means, then the fact that Horn achieved a legitimately good end — the safeguarding of his own life — justifies the intentional killing that secured it.
Catholic moral teaching, however, rejects consequentialism in favor of the rule of double effect. And this rule, when applied to self-defense, demands that no more than the minimum amount of force necessary may be used to stop the threat. The Catechism quotes Aquinas, "If a man in self-defense uses more than necessary violence, it will be unlawful: whereas if he repels force with moderation, his defense will be lawful."
The problem in the Horn case is that Horn used more than necessary violence. In fact, in his situation, violence was not necessary at all. The surest way Horn could have defended himself against the burglars would have been to simply stay inside. Horns' actions are indefensible under the rule of double effect.
Earlier in this space, I argued that Horn's primary motivation was not self-defense at all. Though the details considered by the grand jury are sealed, it apparently concluded that self-defense was the justifying principle for Horn. But even if it qualifies as self-defense, it does not qualify as a morally acceptable action. Horn may not be a criminal, but he is culpable.