The authors are Jim Searcy and Ed Parker
When and how are we allowed, morally, to use lethal force to defend our lives, loved ones, and property?
If you have been wondering about where to draw those lines this article will help.
Here is the Catholic view of Self Defense: From the Catholic Encyclopedia of 1917
Ethically the subject of self-defense regards the right of a private person to employ force against any one who unjustly attacks his life or person, his property or good name. While differing among themselves on some of the more subtle and less practical points comprised in this topic, our moralists may be said to be unanimous on the main principles and their application regarding the right of self-defense. The teaching may be summarized as follows:
Defense of life and personEveryone has the right to defend his life against the attacks of an unjust aggressor. For this end he may employ whatever force is necessary and even take the life of an unjust assailant. As bodily integrity is included in the good of life, it may be defended in the same way as life itself. It must be observed however that no more injury may be inflicted on the assailant than is necessary to defeat his purpose. If, for example, he can be driven off by a call for help or by inflicting a slight wound on him, he may not lawfully be slain. Again the unjust attack must be actually begun, at least morally speaking, not merely planned or intended for some future time or occasion. generally speaking one is not bound to preserve one's own life at the expense of the assailant's; one may, out of charity, forego one's right in the matter. Sometimes, however, one may be bound to defend one's own life to the utmost on account of one's duty of state or other obligations. The life of another person may be defended on the same conditions by us as our own. For since each person has the right to defend his life unjustly attacked, what he can lawfully do through his own efforts he may also do through the agency of others. Sometimes, too, charity,natural affection, or official duty imposed the obligation of defending others. A father ought, for example, to defend the lives of his children; a husband, his wife; and all ought to defend the life of one whose death would be a serious loss to the community. Soldiers, policemen, and private guards hired for that purpose are bound injustice to safeguard the lives of those entrusted to them.
Defense of propertyIt is lawful to defend one's material goods even at the expense of the aggressor's life; for neither justice nor charity require that one should sacrifice possessions, even though they be of less value than human life in order to preserve the life of a man who wantonly exposes it in order to do an injustice. Here, however, we must recall the principle that in extreme necessity every man has a right to appropriate whatever is necessary to preserve his life. The starving man who snatches a meal is not an unjust aggressor; consequently it is not lawful to use force against him. Again, the property which may be defended at the expense of the aggressor's life must be of considerable value; for charity forbids that in order to protect ourselves from a trivial loss we should deprive a neighbor of his life. Thefts or robberies, however, of small values are to be considered not in their individual, but in their cumulative, aspect. A thief may be slain in the act of carrying away stolen property provided that it cannot be recovered from him by any other means; if, for example, he can be made to abandon his spoil through fright, then it would not be lawful to shoot him. If he has carried the goods away to safety he cannot then be killed in order to recover them; but the owner may endeavor to take them from him, and if the thief resists with violence he may be killed in self-defense.
HonorSince it is lawful to take life in the legitimate defense of one's material goods, it is evidently also lawful to do so in defense of chastity which is a good of a much higher order. With regard to honor or reputation, it is not lawful to kill one to prevent an insult or an attack upon our reputation which we believe he intends, or threatens. Nor may we take a life to avenge an insult already offered. The proceeding would not be defense of our honor or reputation, but revenge. Besides, in the general estimation honor and reputation may be sufficiently protected without taking the life of the offender.
And here is the writing of Saint Thomas Aquinas on the subject:
If you have never read St. Thomas in his Summa Theologica then you need to know the format. Saint Thomas always puts forth the arguments AGAINST the premise, then answers them one by one and with a summation.
Article 7. Whether it is lawful to kill a man in self-defense?
Objection 1. It would seem that nobody may lawfully kill a man in self-defense. For Augustine says to Publicola (Ep. xlvii): "I do not agree with the opinion that one may kill a man lest one be killed by him; unless one be a soldier, exercise a public office, so that one does it not for oneself but for others, having the power to do so, provided it be in keeping with one's person." Now he who kills a man in self-defense, kills him lest he be killed by him. Therefore this would seem to be unlawful.
Objection 2. Further, he says (De Lib. Arb. i, 5): "How are they free from sin in sight of Divine providence, who are guilty of taking a man's life for the sake of these contemptible things?" Now among contemptible things he reckons "those which men may forfeit unwillingly," as appears from the context (De Lib. Arb. i, 5): and the chief of these is the life of the body. Therefore it is unlawful for any man to take another's life for the sake of the life of his own body.
Objection 3. Further, Pope Nicolas [Nicolas I, Dist. 1, can. De his clericis] says in the Decretals: "Concerning the clerics about whom you have consulted Us, those, namely, who have killed a pagan in self-defense, as to whether, after making amends by repenting, they may return to their former state, or rise to a higher degree;know that in no case is it lawful for them to kill any man under any circumstances whatever." Now clerics and laymen are alike bound to observe the moral precepts. Therefore neither is it lawful for laymen to kill anyone in self-defense.
Objection 4. Further, murder is a more grievous sin than fornication or adultery. Now nobody may lawfully commit simple fornication or adultery or any other mortal sin in order to save his own life; since the spiritual life is to be preferred to the life of the body. Therefore no man may lawfully take another's life in self-defense in order to save his own life.
Objection 5. Further, if the tree be evil, so is the fruit, according to Matthew 7:17. Now self-defense itself seems to be unlawful, according to Romans 12:19: "Not defending [Douay: 'revenging'] yourselves, my dearly beloved." Therefore its result, which is the slaying of a man, is also unlawful.
On the contrary, It is written (Exodus 22:2): "If a thief be found breaking into a house or undermining it, and be wounded so as to die; he that slew him shall not be guilty of blood." Now it is much more lawful to defend one's life than one's house. Therefore neither is a man guilty of murder if he kill another in defense of his own life.
I answer that, Nothing hinders one act from having two effects, only one of which is intended, while the other is beside the intention. Now moral acts take their species according to what is intended, and not according to what is beside the intention, since this is accidental as explained above (43, 3; I-II, 12, 1). Accordingly the act of self-defense may have two effects, one is the saving of one's life, the other is the slaying of the aggressor. Therefore this act, since one's intention is to save one's own life, is not unlawful, seeing that it is natural to everything to keep itself in "being," as far as possible. And yet, though proceeding from a good intention, an act may be rendered unlawful, if it be out of proportion to the end. Wherefore if a man, in self-defense, uses more than necessary violence, it will be unlawful: whereas if he repel force with moderation his defense will be lawful, because according to the jurists [Cap. Significasti, De Homicid. volunt. vel casual.], "it is lawful to repel force by force, provided one does not exceed the limits of a blameless defense." Nor is it necessary for salvation that a man omit the act of moderate self-defense in order to avoid killing the other man, since one is bound to take more care of one's own life than of another's. But as it is unlawful to take a man's life, except for the public authority acting for the common good, as stated above (Article 3), it is not lawful for a man to intend killing a man in self-defense, except for such as have public authority, who while intending to kill a man in self-defense, refer this to the public good, as in the case of a soldier fighting against the foe, and in the minister of the judge struggling with robbers, although even these sin if they be moved by private animosity.
Reply to Objection 1. The words quoted from Augustine refer to the case when one man intends to kill another to save himself from death. The passage quoted in the Second Objection is to be understood in the same sense. Hence he says pointedly, "for the sake of these things," whereby he indicates the intention. This suffices for the Reply to the Second Objection.
Reply to Objection 3. Irregularity results from the act though sinless of taking a man's life, as appears in the case of a judge who justly condemns a man to death. For this reason a cleric, though he kill a man in self-defense, is irregular, albeit he intends not to kill him, but to defend himself.
Reply to Objection 4. The act of fornication or adultery is not necessarily directed to the preservation of one's own life, as is the act whence sometimes results the taking of a man's life.
Reply to Objection 5. The defense forbidden in this passage is that which comes from revengeful spite. Hence a gloss says: "Not defending yourselves--that is, not striking your enemy back."
Here is the Catholic view of Just War: From the Catholic Encyclopedia of 1917
War, in its juridical sense, is a contention carried on by force of arms between sovereign states, or communities having in this regard the right of states. The term is often used for civil strife, sedition, rebellion properly so called, or even for the undertaking of a State to put down by force organized bodies of outlaws, and in fact there is no other proper word for the struggle as such; but as these are not juridically in the same class with contentions of force between sovereign states, the jurist may not so use the term.
However, a people in revolution, in the rare instance of an effort to re-establish civil government which has practically vanished from the community except in name, or to vitalize constitutional rights reserved specifically or residuarily to the people, is conceded to be in like juridical case with a State, as far as protecting its fundamental rights by force of arms.
John Locke on the right of revolution:
The arbitrary use of authority is called tyranny. Such is the tyranny of an absolute monarch, of a council, of a class, or of a majority. The liberty of the subject is based on the doctrine that the State is not omnipotent. Legally omnipotent every State must be, but not morally. A legal enactment may be immoral, and then it cannot in conscience be obeyed; or it may be ultra vires, beyond the competence of the authority that enacts it, in which case compliance with the law is not a matter of obedience, but of prudence. In either case the law is tyrannical, and "a tyrannical law, not being according to reason, is not, absolutely speaking, a law, but rather a perversion of law" (St. Thomas, Summa Theol., I-II.92.1 ad 4). Man is not all citizen. He is a member, a part of the State, and something else besides. "Man is not subservient to the civil community to the extent of his whole self, all that he is and all that he has" (St. Thomas, Summa Theol., I-II.21.4 ad 3). To say nothing of his eternal interests in his relations with his Maker, man has even in this life his domestic interests in the bosom of his family, his intellectual and artistic interests, none of which can be called political interests. Social and political life is not the whole of human life. Man is not the servant of the State in his every action. The State, the majority, or the despot, may demand of the individual more than he is bound to give. Were human society a conventional arrangement, were man, being perfectly well off in isolation from his fellows, to agree by way of freak to live in community with them, then we could assign no antecedent limits to civil authority. Civil authority would be simply what was bargained for and prescribed in the arbitrary compact which made civil society. As it is, civil authority is a natural means to a natural end and is checked by that end, in accordance with the Aristotelean principle that "the end in view sets limits to the means" (Aristotle, Politics, I, 9). The immediate end of civil authority is well set forth by Francisco Suárez (De legibus, LII, xi, 7) as "the natural happiness of the perfect, or self-sufficient, human community, and the happiness of individuals as they are members of such a community, that they may live therein peaceably and justly, with a sufficiency of goods for the preservation and comfort of their bodily life, and with so much moral rectitude as is necessary for this external peace and happiness". Happiness is an attribute of individuals. Individuals are not made happy by authority, but authority secures to them that tranquillity, that free hand for helping themselves, that restful enjoyment of their own just winnings, which is one of the conditions of happiness. Nor does authority make men virtuous, except according to that rough-hewn, outline virtue, which is called "social virtue", and consists mainly of justice. When the ancients spoke of "virtue" being the concern of the State, they meant justice and efficiency. Neither the virtue nor the happiness of individuals is cared for by the State except "as they are members of the civil community". In this respect, civil differs from domestic, or paternal, authority. The father cares for the members of his household one by one, singly and individually. The State cares for its members collectively, and for the individual only in his collective aspect. Hence it follows that the power of life and death is inherent in the State, not in the family. A man is hanged for the common good of the rest, never for his own good.