In Catholic social teaching, there is a foundational teaching that is ignored and rejected by many Christians, even Catholics striving to practice their faith. It is a teaching that deserves to be reckoned as among the most important contributions of the Catholic faith to social issues. This teaching is a bulwark of the culture of life and the inviolability of marriage. This teaching prevents emotion and utilitarianism from destroying the moral fabric of our Catholic faith. The teaching to which I allude is a traditional teaching with deep roots in our faith, “malum in se,” which is accurately translated into English as “wrong in itself.” That is, there are certain actions that are wrong by the very nature of the object chosen, irrespective of whatever consequences ensue from the action or whatever intention inspires them. The Catechism of the Catholic Church states this teaching beautifully as follows: “It is therefore an error to judge the morality of human acts by considering only the intention that inspires them or the circumstances (environment, social pressure, duress, or emergency, etc.) which supply their context. There are acts which, in and of themselves, independently of circumstances and intentions, are always gravely illicit by reason of their object; such as blasphemy and perjury, murder and adultery. One may not do evil so that good may result from it.” 
To be more precise, there are three sources of morality in Catholic teaching: the object chosen, the intention, and the circumstances.  If all three of these are not good, the action itself is not good. Circumstances vary and intention may require knowledge of the human heart, which only God possesses in fulness, but one can confidently assert that certain objects are always and everywhere wrong, no matter how much good derives from them or how well intentioned they are. The Catechism lists 4 examples: blasphemy, an offense against the sanctity of God’s name; perjury, an offense against the truth; murder, an offense against the sacredness of human life; and adultery, an offense against the sacredness of marriage. There can never be and never will be a circumstance or an intention that makes any single one of these actions morally licit. Blasphemy, perjury, murder, and adultery are “malum in se,” wrong in and of themselves.
This teaching is corroborated by Saint Pope John Paul the Great in Veritatis Splendor, “Reason attests that there are objects of the human act which are by their nature ‘incapable of being ordered’ to God, because they radically contradict the good of the person made in his image. These are the acts which, in the Church’s moral tradition, have been termed ‘intrinsically evil’ (intrinsece malum): they are such always and per se, in other words, on account of their very object, and quite apart from the ulterior intentions of the one acting and the circumstances.”  This teaching is further corroborated by soon-to-be Saint Pope Paul VI in Humanae Vitae: “In truth, if it is sometimes licit to tolerate a lesser evil in order to avoid a greater evil or to promote a greater good, it is not licit, even for the gravest reasons, to do evil so that good may follow therefrom; that is, to make into the object of a positive act of the will something which is intrinsically disordered, and hence unworthy of the human person, even when the intention is to safeguard or promote individual, family or social well-being. Consequently[,] it is an error to think that a conjugal act which is deliberately made infecund and so is intrinsically dishonest could be made honest and right by the ensemble of a fecund conjugal life.” Indeed, Scripture itself teaches us that we may not do evil so that good comes from it (Romans 3:8).
Now there are many situations where the vital importance of this teaching becomes clear. Let us take the example of the married woman who is told by a man not her husband that if she does not make love to him, he will kill 10 people. Is it morally justifiable for the woman to commit adultery against her husband to save 10 lives? Let us suppose that the woman chooses to commit adultery to save the 10 people. Since adultery is “malum in se,” morally wrong independent of whatever good results from the action, even saving the lives of ten innocent people, the woman’s action is immoral. Her intention was good, and her good intention can certainly mitigate her moral culpability, but she committed adultery, she intentionally had sexual relations with a man that was not her husband. It is inaccurate to say she was raped. She was not raped. Though there is certainly coercion, she consented or chose the act of adultery, and that choice is never morally permissible because it is inherently contrary to the natural unity of marriage.
For those who argue that the woman acted morally, let us inquire further. Would it have been morally permissible for her to commit adultery against her husband to save one life? How about two lives? How about ten, or a hundred, or a million lives? Who determines the correct number of lives that need to be saved to justify adultery? But for the teaching of the Church that adultery is “malum in se,” it would be impossible to have moral certainty about the woman’s conduct. Thankfully, the Church saves us from such subjective equivocations by getting to the heart of the matter. Adultery, the intentional decision to have sex with a person that is not your spouse, can never be justified because the object is evil. Otherwise, evil people could simply negotiate until any action becomes morally acceptable. An evil person could say: “Oh ok, you are not willing to commit adultery to save one life, while how about if I kill ten people? Then will you commit adultery?” You see, the truth is, those who argue in favor of the woman committing adultery do not really believe in right and wrong as objective matters. For them, right and wrong is always dependent on the circumstance. They can never say “adultery is wrong” because there will always be circumstances that would justify adultery. This kind of thinking lends itself to moral relativism because once you reject that adultery is always wrong, it is impossible to make rational decisions about when adultery is permissible. And just like that, the entire objectivity of moral actions is dissolved and the strong edifice of Catholic social teaching founded on the objective Truth of Jesus Christ is seriously weakened.
There are perhaps some who believe in “malum in se” in the abortion context but not in the marriage context. But this is utterly illogical and contrary to the unity of Catholic social teaching. One cannot logically say: “abortion is always wrong,” but adultery is sometimes justified. If it is always wrong to take an innocent human life, it is always wrong to intentionally violate your marriage. This must be the case because the sanctity of human life is the fruit and gift of marriage. Both are equally worthy of protection. If apples are worthy, so too are apple trees; if human life is worthy of protection, and it is, it is because the union known as marriage that produces human life is worthy of protection. Because marriage and human life are inseparably connected in God’s plan, it is utterly illogical to give the latter more protection than the former. Either you affirm that abortion and adultery are always and everywhere wrong, or you deny this to the detriment of both human life and marriage. There is no logical middle ground.
Of course, the principle of “malum in se” has implications beyond abortion and adultery. It has implications for contraception, in vitro fertilization, the cloning of human beings, the protection of conscience rights, and more. In all these areas, the objectivity of moral principles will give way to the relativism of subjective preferences if we disregard the Church’s wise teaching of “malum in se.” So the next time you are tempted to justify an action that is intrinsically immoral, remember that God is always good and is, in fact, the highest good, and would never ask you to do evil, no matter how much good comes from it.
### Catechism of the Catholic Church, 1756.  Catechism of the Catholic Church, 1750.  Pope John Paul II, Encyclical letter Veritatis Splendor, 80.  Romans 3:8: “That would be the same as saying: Do evil as a means to good. Some slanderers have accused us of teaching this, but they are justly condemned” (The Catholic Truth Society (CTS) New Catholic Bilble).  In Ephesians 3:8, St. Paul discusses the goodness of God in terms of the “infinite treasure of Christ,” who is God (CTS New Catholic Bible). In Mark 10:18, Jesus says explicitly, “No one is good but God alone” (CTS New Catholic Bible).