10. May a married couple use barrier contraceptives to prevent disease transmission?

No. The use of contraception deprives the sexual act of the procreative meaning and is therefore intrinsically evil and always gravely immoral. When an act is intrinsically evil, neither a good intention, nor dire circumstances, can cause the act to become moral.

Catechism of the Catholic Church: "Legitimate intentions on the part of the spouses do not justify recourse to morally unacceptable means (for example, direct sterilization or contraception)." (CCC, n. 2399)

The end does not justify the means. And so the intended end of preventing disease transmission does not justify the use of an intrinsically evil means, contraception. Acts which are not intrinsically evil may be moral, depending on intention and circumstances. But acts which are intrinsically evil are always immoral, regardless of intention and circumstances.

Pope John Paul II: "But the negative moral precepts, those prohibiting certain concrete actions or kinds of behavior as intrinsically evil, do not allow for any legitimate exception. They do not leave room, in any morally acceptable way, for the 'creativity' of any contrary determination whatsoever. Once the moral species of an action prohibited by a universal rule is concretely recognized, the only morally good act is that of obeying the moral law and of refraining from the action which it forbids." (Veritatis Splendor, n. 67.)

The moral species is the type of act in terms of morality; it is the essential nature of the act according to the eternal moral law of God. Contraception is always gravely illicit because it is a type of act that is inherently contrary to the law of God on human sexuality. The deprivation of the procreative meaning causes the moral object of contracepted sexual acts to be evil, and the act of using contraception to be, in and of itself, gravely illicit. Even good intentions and dire circumstances cannot cause an inherently illicit act to become moral or justifiable.

The Catechism of the Catholic Church: "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." (CCC, n. 1756.)

Pope John Paul II: "No circumstance, no purpose, no law whatsoever can ever make licit an act which is intrinsically illicit, since it is contrary to the Law of God which is written in every human heart, knowable by reason itself, and proclaimed by the Church." (Evangelium Vitae, n. 62.)