Joe Carter has some great thoughts on sex and Wendell Berry, most of which I agree with.
The central premise is taken from an essay that we've referenced 'round here before, namely that the divorce between the body and the soul mechanized the body and led to an industrialized approach to sex oriented around maximizing pleasure.
Most of Joe's practical advice is right on the money. But he goes awry when he hits #6:
6. Sex may be a joy and a sanctuary but it is also a marital duty. It is the primary physical method God provides in order to deepen and strengthen the union of a man and a woman. Forgoing sex for long periods of time can be a form of disobedience. If we are physically able, we should give ourselves to our spouses. We are the sole means by which they are able to properly meet that physical need. Denying our spouse food or sleep would be cruel and unjust. Withholding sex is no different.
Yes to a duty, and yes to the sinfulness of withholding sex. Doing that reduces sex to a manipulative tool and destroys the integrity of the act.
But Joe is a little too quick to draw a straight line between sex, food, and sleep. In point #2, Joe points out (rightly) that sex is a form of communication rather than strictly a technique. But as communicative, it seems sex is a bodily act distinct from other bodily pleasures or needs. Like all communication, there is an element of freedom in the act that suggests that sex is not motivated by the same laws that motivate us to find food--on which our material well-being actually does depend.
The point has practical ramifications, especially for single people. If sex is a necessity along the lines of food, then we should expect us to have a morally licit outlet for it, regardless of our marital status. While there might be a case that masturbation is licit, the easier way through is to reject the premise. Sex simply isn't a necessity in the same way that food is.
I'll make the case for rejecting that premise theologically.
Sex often seems like a necessity because it is frequently tied to certain biological pleasures and urges which have a strong motivational pull, and because the propagation of the species depends (for now, at least) upon the act.
But if we stopped there, sex wouldn't be a distinctly human form of communication. But sex as a human act is best construed as an act of self-giving in which man--as man and woman--freely gives himself to the other and opens himself to receiving the gift of the other. For Christians, the normative account is in the Garden of Eden, which suggests that sex bears witness to the order of creation.
But singleness points in the other direction. It bears witness to the eschatological life (in which we shall neither "marry nor be given in marriage") that was inaugurated by Christ in his resurrection. Rather than destroying the order of creation and the goodness of sex and its pleasures, it establishes the biological on its properly human foundation: the freedom to give ourselves to God, who then enables and frees us to give ourselves to others. In that sense, the vocation of singleness not only disestablishes sex from being a need in the way food is, but points us toward the transcendent basis of marriage (and sex itself): it is a union that is oriented ultimately toward God.
What does this mean, practically speaking?
Single people are, in fact, human. My single friends tell me this is unfortunately still a question. It shouldn't be. In fact, any church where singleness is not treated as a full and acceptable vocation within the family of God does not value marriage properly, for it rejects one of the primary witnesses to the church's eschatological life and one of the primary witnesses to marriage's transcendent basis.
Sex is good. But it is not necessary. And the distinction must be kept in mind, lest we unwittingly undermine the way in which sex and marriage witness to the reality of the Gospel.
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Addendum: My thoughts and language are heavily influenced here by JP2. Just thought I'd mention that.