What and Why is the Church Teaching on Sexual Morality? (CCC 2337-2359, 2380-2391)
(For information concerning general moral principles, please see the short course in morality.)
What
The Catholic Church teaches that sexuality is a gift from God and that sex – when used in the correct manner – is in fact a source of holiness and sanctification. The correct manner depends on three factors;
Between a man and a woman (this condemns homosexual unions)
Open to the transmission of new life (this condemns contraception)
Within a valid marriage
Accordingly, the Church condemns fornication (sex between unmarried partners), adultery (sex with someone who is not your spouse), masturbation (deliberate stimulation of the genitals to gain sexual pleasure), anal and oral sex, homosexual sex, sex with multiple partners and contraception. The Church also condemns pornography, prostitution and any form of sexual activity which seeks to degrade the participants or weaken the marriage bond. In addition, the Church condemns provocative and immodest dress and actions in both men and women.
The Church does not choose to condemn or legislate against any particular sexual position or activity which does not fall into these categories. The Church also, most importantly, does not condemn sex as sinful and certainly does not suggest that physical pleasure or sexual attractiveness and beauty are bad. The Church teaches precisely the opposite – that sexual pleasure, attractiveness and beauty are gifts from God which, correctly used, can lead to greater holiness (either through correct and sacramental participation or through chastity).
The most relevant Church document on this subject is Pope John-Paul II's Theology of the Body which has been excellently explained in a number of works by Christopher West. These are strongly recommended to the apologist or, indeed, anyone wishing to learn more.
Why
Much of the Church teaching on sexual morality is because of the Church teaching on abortion, contraception, homosexuality and marriage, and so consulting those articles is recommended.
Fornication is condemned because it is sex outside of marriage (which is the only correct place for it). A union outside of marriage does not have the binding, sacramental quality of matrimony and therefore cannot truly lead to a family in the same way. This means that any children conceived by the sexual act (and, indeed, the mother and father themselves) do not benefit from the stability of the family environment. There is a greater chance that a child conceived via fornication will be aborted or neglected by one or more parents, as the parents had not made a covenant commitment to each other.
Fornication is also likely to involve contraception, which is condemned by the Church, and the promiscuous fornication prevalent in our society leads to a denigration of both woman and men, viewing them as nothing more than objects of sexual pleasure rather than creatures made in the image and likeness of God.
Adultery is condemned for the same reasons as fornication, but also because it weakens the marriage bond, is the breaking of a solemn covenant (which carries very real consequences), and generally speaking involves other sins (lying being the most obvious). It damages the family and injures the both the adulterer, the person he or she is having sex with, and any spouses or children involved.
Sex with multiple partners is condemned as a form of fornication or adultery (generally speaking, it is both) and additionally because such activities generally involve contraception and homosexual activity. Sex with multiple partners in also condemned because sexual activity is a wholesale and complete giving of oneself to a single person. This is impossible in sexual activity with multiple partners (either simultaneously, or separately) and not only is this a sinful act in itself, but it actually damages the individuals' ability to form a meaningful and genuine loving relationship.
Forms of sexual activity which are not open to the transmission of new life (oral and anal sex, homosexual sex and so forth) are condemned because they divorce the procreative aspect of sex from the pleasurable aspect, something which cannot be done. They are, in essence, simply a form of contraception. A number of these activities (most especially sodomy) are physically harmful as the human body is not designed to perform them – this is viewed as causing physical harm to a human body (even if it is one's own) which is not permitted as the body is the temple of the Holy Spirit (I Corinthians 6:19-20).
The condemnation against pornography and prostitution is for multiple reasons. Generally speaking, the production of pornography involves one or more of the sexual activities condemned above (contraception, homosexuality, anal and/or oral sex, multiple partners, adultery and fornication) and so the very act of making pornography is morally wrong. Those who profit from pornography and prostitution are also rightly condemned as they are benefiting from the degradation of others and are encouraging them in sin. The objective guilt of pornographic actors and prostitutes can be lessened by coercion and force applied to them (blackmail, threats, lack of other employment) and this will increase the objective guilt of those forcing them to participate. This includes the men (or women) who visit prostitutes or view pornographic materials (even if they do not pay for them – it is still encouraging the production of pornography).
It is wrong to use prostitutes because it involves adultery or fornication at the very least, damages the family bond, exploits the prostitute and so forth. The viewing of pornography is condemned because it exploits the actors and participants, but also because it invades and encourages an invasion of the sexual act (the most intimate communion between a man and a woman) by a third party. It degrades the sexual act in the eyes of the viewer, and damages his (or her) ability to have a meaningful and genuine sexual relationship.
The viewing of pornography (and, indeed, looking at other human beings in a deliberately lustful fashion and dwelling on those thoughts and encouraging them) is rightly condemned following the instructions of Christ in Matthew 5:28 which equates deliberately lustful thoughts with adultery. It is also condemned for simple practical reasons – it leads to temptations and degrades the individual who is being lusted over. A man (or woman) who is constantly thinking lustful thoughts damages his (or her) ability to respond correctly to sexual love, seeing members of the opposite sex simply as objects for his (or her) personal gratification.
Immodest dress is condemned, and is defined as dressing in a manner likely to arouse sexual interest or with the intention of arousing sexual interest in a situation where this is inappropriate (generally speaking, where it will arouse sexual interest in individuals other than the person's spouse). The Church condemns this as tempting other individuals into sin. While this does not absolve the sinner of his guilt, it means that the tempter shares in some of that guilt. The Church does not condemn those who dress provocatively or sexily in the appropriate situation (in the privacy of their own homes, with their spouses) – such actions can and do increase the attraction felt by the spouses and strengthen the sexual and marriage bond. In a similar fashion, the Church teaches that to dress attractively is not a sin – it is adorning the human form (which is one of the most beautiful forms) and presenting God's creation in the best light. The Church condemns inappropriately provocative and sexually-suggestive dress.
Care must be taken in judging what is provocative – certain individuals (most often men) have particular fetishes of dress and behavior which are not normally considered to be sexually attractive. A person incurs no guilt if her or she (in all innocence) dresses in a manner which is not normally considered provocative but does, in fact, arouse the lust of a disordered individual. Care must be taken, however, that individuals seeking to appear attractive do not dress immodestly or inappropriately.
Magazines, publications, clothing catalogs, television programs, movies, internet sites and the like which – while not technically speaking pornographic – present immodest dress or support, advocate or encourage a promiscuous lifestyle (or any other sort of sexual sin) are condemned for the same reason of leading to temptation.
Masturbation is condemned because it divorces the sexual act from everything but the physical pleasure. It is a completely and utterly selfish act which treats the object of lust with even less respect than fornication does (the fantasy object is often viewed, in the imagination of the masturbator, as nothing more than an entirely compliant source of sexual pleasure, without any will of his or her own). It is the final expression of lustful thoughts, and most often involves pornography or immodest dress or behavior. Masturbation is specifically condemned by God's killing of Onan in Genesis 38:9-10. Many liberal theologians will say that God killed Onan for refusing to engage in a Levirite marriage with his brother's widow, but we learn in Deuteronomy 25:5-10 that the penalty for refusal is not death.
Unions between human beings and animals are condemned following Leviticus 20:15-16. Not only are these actions not between a man and a woman, outside of marriage and not open to the transmission of new life, but they are gravely disordered because they degrade the human person who is made in the image and likeness of God (Genesis 1:26) and who has dominion over the animal kingdom (Genesis 1:28). This dominion should never be understood as a right to use the animals for whatever purpose we desire (especially when that purpose is morally wrong) but rather that we are placed above the animals. Humanity should not degrade the only creature made in the image and likeness of God by unnatural unions with lower animals.