The following comes from a February 20 Catholic World Report article by Janet E. Smith:
It confuses many that the officials of the Church many decades ago permitted nuns in the Congo who were in danger of being raped to take hormones that prevent ovulation (which is what the “pill” does). In this case the hormones would be taken with the intent of avoiding a pregnancy, but not a pregnancy that would be the result of a spousal act of sexual intercourse. They would not be altering the purpose of a spousal act of sexual intercourse.
Rather, they would be defending themselves against the possible consequences of an act of rape. Keep in mind that it is justifiable for a woman to inflict great physical harm, even death, on a man threatening rape. Her act of killing the rapist is not justified as a “lesser evil” because killing is not a lesser evil than enduring rape. Rather, her act is an act of just and moral self-defense.
Thus, for a woman to do something to prevent a rapist’s sperm from uniting with her ovum is a part of justifiable self-defense. Her act has nothing to do with violating God’s plan for sexuality. She is not choosing to use contraception to prevent a spousal act of sexual intercourse from achieving its natural end. She is not refusing to make a complete gift of herself to her spouse. She is fending off a rapist and all his physicality. Clearly, her use of ovulation-suppressing hormones is not an act of contraception. (A good source for information about the history/reasoning concerning the nuns in the Congo is Fr. Edward Bayer’s Rape Within Marriage (1985), pp. 82-3)
The principle of choosing the lesser evil does not justify a woman using contraception to prevent a pregnancy because she fears the child may suffer some harm during the pregnancy. Here a woman is choosing to do something immoral to prevent harm. This choice violates the fundamental principle that we must never do moral evil to achieve good. She would be intending to thwart the purpose and meaning of the sexual act in order to protect any child conceived from harm, but she is doing harm—to the marital act and her marital relationship—by using contraception to prevent a pregnancy.
There are all sorts of “harm” that spouses may wish to attempt to avoid by using contraception. In fact, one suspects that there is always some harm spouses are trying to avoid by using contraception—harms such as financial stress, inconvenience, threats to the mother’s health, sexual frustration, etc. The Church has never taught that if the harms are serious enough, it is permissible to use contraception, for that would be choosing to do moral evil to avoid harm.
To suggest that some “emergency” or “special situation” would permit a person in conscience to use contraception does not align with Catholic moral theology. For spouses to use contraception is always wrong. How can any emergency or special situation justify what is always wrong? It is an improper use of conscience to use it to discern that it is moral to do what is intrinsically wrong in special situations. One job of the conscience is precisely to enable a person to honor moral norms in special situations. In emergencies or special situations we are not permitted, for instance, directly to kill innocent human beings even if great good could come from that death. Martyrdom is precisely a result of the refusal to do something that is morally wrong in an “emergency” or “special situation.”