It is not simply an anti-pleasure motive which causes Christianity to regard extra-marital sex as a sin, and therefore to prohibit it (though some truncated brands of Christianity have distorted this concept and wrongly frowned upon pleasure qua pleasure).
Sex is a deeply mystical, metaphysical thing, and designed by God to be so. To have sex with a person is to literally become "one flesh" with them (Matt 19:5-6, 1 Cor 6:12-20) -- not just physically, but "mystically" and spiritually as well. So sex profoundly unifies people. Wine and opera don't do that, except in a superficial sense! There is an ontological transformation which takes place when intercourse occurs.
It is a very strong emotional bond -- as all know who have experienced it. For this reason, orthodox Christianity has always held that sex outside the marital commitment is sinful and wrong, because it is (when all is said and done, and in essence, if not always in deliberate intent) an exploitation of the other for the sake of pleasure. It assumes a physical oneness before the appropriate complete spiritual oneness of life that occurs in marriage has been committed to. It's (literally) putting the cart before the horse.
The denial of this has led to a host of problems, whether divorce or child or spousal abuse or one-parent families, or AIDS, or all the mental and emotional agonies resulting from broken relationships.
It is not "love" which urges one to proceed to sex before commitment to the whole person for life. Even our natural instincts tell us that the two ought to go together. Christianity has it exactly right. C.S. Lewis, in his marvelous book The Four Loves, wrote about how people in love instinctively start talking about being together forever, loving only each other, how the desired is the greatest, most fabulous person in the world, etc. They know instinctively -- apart from Christian moral theology -- that commitment goes hand-in-hand with erotic desires and fulfillments.
Otherwise, it just doesn't work. Not to be overly-blunt, but apart from this commitment the woman is reduced to (conservative Jewish talk-show host and psychologist Dr. Laura Schlesinger's term) an "unpaid prostitute." The man likewise becomes a mere object for pleasure. The feminists of all people should immediately see how premarital sex -- far from being "liberating" for the woman -- promotes and positively encourages all the age-old unmarried male exploitations, manipulative sexual/romantic games, and perceptions of women as primarily sexual objects.
The truly "strong woman" whose self-image is properly grounded in God and Christian (even natural law) morality, resists all that, knowing that her sexual allure and feminine appeal to a man is the greatest power she has to "pressure" the man into committing himself to her for a lifetime (by resisting his advances before such commitment). That's just the way it is. And if you can't
trust a future mate (particularly a man) to be strong and to resist sexual temptation before marriage (proven by chastity in the dating relationship), how can you trust them after the wedding -- when even greater temptations present themselves, and where it takes a great deal of effort to keep the "flame" going?
The non-Christian notion of marriage and co-habitation, therefore, is a ticking time-bomb, and offers little emotional security or stability, especially for women. The free-sex "ethos" inevitably punishes women, whereas unscrupulous playboys and philandering Bill Clinton-types can engage in their abuses with the least consequence (though assuredly not without none -- they are not happy in the long run, either).
Clearly, sex means much more between a man and a woman than it does between two hogs or rhinos. We feel a beautiful oneness, we feel like we have opened up the most intimate aspects of ourselves to another human being - and are therefore made quite vulnerable (the stakes are very high: it's either "heaven" or "hell" at that point).
For precisely that reason, God designed sex to be appropriate and entirely good and positive and safe only within the context of a lifelong marital bond and commitment. All recent sociological experience bears this out. The Christian has far more to appeal to for his case than the Bible or papal proclamations. False moralities always refute themselves in their disastrous historical results. We are living through one such period.
Even secular surveys of married couples and their enjoyment of sex consistently show that Christian couples (especially those who were virgins until they were married) experience a significantly higher level of pleasure in sex than those who are non-Christians, or who have
"experimented" before marrying. The truth is exactly the opposite of the cultural myths promulgated by those who have a stake in the promulgation of the sexual revolution. Traditional, orthodox Christians -- pilloried as being supposedly against sex -- are in fact enjoying it qualitatively and quantitatively much more than their "liberated, free" counterparts.
The irony of that is delicious, but it saddens me that so many fall for these secularist, feminist, post-Christian lies, thus dooming themselves to almost certain misery. Sometimes it takes a lot for people to wake up to moral sanity -- even the collapse of an entire civilization.
One can even make a "sociological" argument against premarital sex, based strictly on its negative societal consequences:
1) Whatever has harmful consequences for society is "bad" for society.
2) We can determine on many sociological grounds and social indicators that extramarital sex and so-called "free sex" have produced many harmful consequences.
3) Though this doesn't prove that extramarital sex is a sin in and of itself, yet it is entirely consistent with the Christian notion that it is a sin, since Christians believe that sins have harmful personal and societal effects.
Negative consequences flow from the inherent wrongness of premarital sex. Objective evil inexorably leads to further evils (in this case, e.g., abortion and millions of broken lives and homes and a host of other societal ills and sins). But I am not arguing that premarital sex is wrong because of these consequences.
Our society and culture continue to neglect all the negative consequences of premarital and extra-marital sex because it has adopted the humanist free love ethic. Morality is not solely determined by good intentions and the absence of force or malice, etc. There are also absolute moral rules which have been time-tested and which are clearly taught in Scripture.
Sin has consequences. They may not be immediately evident (in the case of sexual sin), but in the long run and in society they will be. We have largely accepted the libertarian or utilitarian myth that we all live to ourselves, and if we don't mean harm to someone, then it is okay to have sex with them. But -- again -- that reduces us to animals and assumes falsely that sex is no different than drinking wine, etc. This is a myth. It is simply untrue -- and, I think, clearly so.
We are refusing to love God if we ignore the moral commands that He has revealed through His Sacred Scriptures and the Sacred Tradition of His Church. We are refusing to love others if in fact we are objectively exploiting them and causing them emotional harm (or worse) in the long run.