1817. Other distinctions of homicide have a bearing on its added or accidental malice.
(a) A new species of sin is added to that of injustice when other virtues are offended against. Thus, the virtue of piety is violated when the victim is a person to whom the slayer owed special respect and devotedness, as in parricide, regicide, fratricide, uxoricide; the virtue of religion is offended when murder is committed in a church.
(b) An aggravating circumstance is added by the greater deliberation with which the homicide is planned, or the greater treachery or cruelty with which it is executed (e.g., assassination, death by starvation). Some circumstances, however, may be morally indifferent, such as the fact that the victim is killed by one kind of poison rather than another.
1818. The Killing of Animals (or Vegetation).—(a) In itself, the killing of animals is not sinful; for animals are made for the use of man. Hence, it is lawful to kill, not only harmful animals, such as those that prey on human beings or breed pestilence or destroy property, etc., but also other animals, when their death is necessary for some good purpose, such as the provision of food, clothing or medicine for man.
(b) In its circumstances, the killing of animals may be sinful, and even gravely sinful, as when one kills the animals of one’s neighbor (Exod, xxii. 10, 11), or hunts against the law, or injures society by prodigal destruction of animal or plant life, or kills animals in cruel ways. The skinning of animals alive, in order to secure finer-looking furs to satisfy the vanity of women, is an inhuman barbarism of the worst type that should be reprobated by everybody.
1819. When Homicide Is Lawful.—Killing of human beings is lawful in two cases. (a) It is lawful when the common safety requires that the State inflict death for a crime (capital punishment); for just as it is lawful to amputate a gangrenous member which threatens to destroy the body, so is it lawful to remove from human society by death an individual who menaces the safety of the community. (b) It is lawful when the safety of an individual demands that he kill an unjust aggressor (self-defense); for a man owes his first duty to his own life in such a case, and the aggressor in making a deadly attack voluntarily assumes the risk of being killed. It is more correct, however, to say here that it is lawful to defend one’s life with resultant death to the offender (as will be explained below, in 1826, 1828, 1834).
1820. Arguments for the Lawfulness of Capital Punishment.—(a) Scripture.—In the Old Testament the death sentence was prescribed for certain more serious crimes, such as murder (“whosoever shall shed man’s blood, his blood shall be shed,” Gen., ix. 6); in the New Testament Our Lord recognizes that the power of a judge to sentence to death comes from above (John, xix. 10), and St. Paul declares that princes do not wield the sword without reason, but act as ministers of God when they punish evil-doers (Rom., xiii. 4).
(b) Tradition.—The Church has always taught the lawfulness of capital punishment and rejected contrary errors, as in the case of the Waldensians condemned by Innocent III.
(c) Reason.—The State has both the duty and the right to promote the common good and to defend it against its enemies, whether by war against external foes or by coercive measures against internal disturbers of the peace. Now, the experience of all the centuries and of all countries has shown that, generally speaking, the lives of law-abiding persons and the general peace are not sufficiently protected unless the supreme penalty be appointed for certain crimes.
1821. Though lawful, capital punishment is not always necessary; for it is a means to an end, and it may be omitted, therefore, when the end can be obtained by the use of other and less severe means.