When we think of the culture wars, we tend to think of sex. And when we think of the most contentious political fronts in the sex wars, we usually think of gay marriage, abortion rights, and pornography. As divisive as those issues remain, a universal human activity may lie at the heart of these contemporary struggles: masturbation. The questions that self-pleasure raises are foundational: to whom do our bodies belong? What is sex for? Tell me how you really feel about masturbation, and I can more or less predict how you'll feel about the more frequently debated "sex war" issues.

Masturbation is almost certainly the most common human sexual practice. Though statistics about private sexual behavior vary widely, there's little dispute that the vast majority of both men and women will masturbate over the course of their lifetimes. Perhaps nothing so universal is discussed with greater embarrassment (or denied with greater frequency). That enduring shame and silence is one reason behind National Masturbation Month, which comes (sorry) to an end next week. First organized by the pioneering sex shop Good Vibrations in 1995 to protest the firing of Surgeon General Joycelyn Elders (who had dared suggest that teaching young people to masturbate could have a place in sex education), the month's events include innumerable education events across the country—and a Masturbate-a-Thon in San Francisco that raises money for charity. The month serves, as Good Vibrations announced in its annual press release, as "a necessary reminder that self-satisfaction is a healthy, accessible form of pleasure engaged in by almost everyone."

The view of masturbation as benign and beneficial is a new one. The Judeo-Christian tradition has long been hostile towards self-pleasure, at least for men. The Talmud compares spilling seed to spilling blood; the Zohar (the central work of Kabbalah) calls it the most evil act a man can commit. The traditional Christian view was no more tolerant; Catholic and Protestant authorities framed masturbation as a deeply sinful (though forgivable) waste of precious semen. Women were left out of these prohibitions for the obvious reason that most male religious authorities didn't consider the possibility that women were capable of or interested in giving themselves orgasms.

The campaign against masturbation became medicalized in the middle of the 19th century. Health reformers like Sylvester Graham (of the cracker) and John Harvey Kellogg (of the cereal) warned against the feminizing and enervating effects of male masturbation, describing it not as a sin but as a habit that could rob boys of their vital life force. At the same time, doctors began to warn of something theologians either hadn't considered or dared to mention: the dangers of female self-pleasure. Beginning in 1858, Dr. Isaac Baker-Brown—the president of the Medical Society of London—began to encourage surgical clitoridectomies to prevent hysteria, epilepsy, mania and even death that would surely follow as a consequence of the stimulation of the clitoris.

Other Victorian-era doctors took a seemingly more enlightened attitude than Baker-Brown. In the early 1880s, Joseph Mortimer Granville patented the first vibrator as a means of quickly inducing therapeutic "paroxysms" (orgasms) as a cure for hysteria in female patients. But Granville wanted those orgasms to take place only under safe medical supervision, thus maintaining medical (and male) control over female pleasure. As Rachel Maines points out in her excellent history of the vibrator, the early medical monopoly on the device was explicitly designed to make solitary self-stimulation with the hand seem unsatisfying by comparison. Granville's vibrator and Baker-Brown's clitoridectomy represent two very different approaches to the same terrifying problem: women's capacity for self-satisfaction.

The 19th century's secularized anxiety about masturbation was rooted in a fearful reaction to women's growing demands for political and economic power. Simply put, doctors and moralists feared that masturbation made men more dependent—and women less so. Kellogg and Graham worried that boys who masturbated would not only lose their physical vitality, but would become more easily influenced and even dominated by women. The boy who could resist pleasuring himself as a teen was learning the strength he'd need not to allow himself to be manipulated and hen-pecked by his future wife. At the same time, Granville, Baker-Brown, and their peers worried that a woman who learned to give herself sexual pleasure might pursue self-sufficiency in other areas. At a time of rising male anxiety about feminist demands for suffrage, female masturbation became an unsettling symbol of women's independence.

More than a century later, masturbation remains a cultural battleground. Many progressives were bewildered by Antonin Scalia's blistering 2003 dissent in Lawrence v Texas, in which he warned that state laws against evils such as "adult incest, prostitution, masturbation, adultery, fornication, and bestiality" might be invalidated as a result of the decision. Why, liberals wondered, was masturbation included on that list? The answer is simple: masturbation remains not only a grave sin in the eyes of the Catholic Church to which Scalia belongs, but its acceptance as benign and healthy is perhaps the foundational error of modern sexual culture.

The contemporary catechism of the church doesn't mention the waste of seed. Rather, heavily influenced by the late John Paul II's "theology of the body," it insists that our sexuality is intended for one purpose: "the relationship of one person to another, in the complete and lifelong mutual gift of a man and a woman." Evangelical Protestants often make the same case; the anti-porn ministry XXX Church teaches that "It is a selfish act that pleases no one but you. God created sex to be between a man and his wife. Not a man and his girlfriend and not a man or woman with himself or herself."

As religious conservatives see it, the great mistake we make when we masturbate is to claim our sexuality as ours alone. All sexual activity must be about "mutual self-giving" between a husband and a wife, the church claims, arguing that masturbation is "an intrinsically and gravely disordered action." Since masturbation is the first sexual act in which most people voluntarily engage, it is in a very real sense the original sexual sin from which all the others—based as they are on this mistaken sense of autonomy—flow. On the right, opposition to the idea of masturbation as an acceptable practice is growing rather than declining. Dr James Dobson, the founder of Focus on the Family, long claimed that the practice was essentially benign. Since his retirement, the organization—a flagship for social conservatism—has changed its tune, now arguing firmly that "self-gratification is inconsistent with the purpose, goal and basic nature of sex. "

It's not just the religious right, of course, that's interested in the "purpose, goal, and nature of sex." In The Ethical Slut, perhaps the best-known "catechism" of progressive sexual morality, Dossie Easton and Janet Hardy make the case that "the fundamental sexual unit is one person; adding more people to that unit may be intimate, fun, and companionable, but it does not complete anybody." Masturbation matters, they argue, not merely because it helps you learn what you want sexually from a partner, but because it helps bring "your locus of control into yourself."

Easton and Hardy's argument is rooted in American feminist thought. More than a century before The Ethical Slut was published, Elizabeth Cady Stanton—a contemporary of doctors Granville and Baker-Brown—made the case for a movement that prioritized autonomy. "The isolation of every human soul, and the necessity of self-dependence, must give each individual the right to choose his own surroundings," she said in her 1892 retirement address; "when we consider the self-dependence of every human soul we see the need of courage, judgment and the exercise of every faculty of mind and body, strengthened and developed by use." Contemporary liberal sexual ethics of the kind that Easton and Hardy espouse grow out of that same feminist insistence on autonomy that so terrified religious leaders and Victorian physicians alike.

Masturbation feels really good. It also can feel really icky, when conditioned feelings of guilt wash over the masturbator as he or she comes down from a post-orgasmic high. That shame may or not be rooted in religion, but it is certainly grounded in the idea that the fundamental sexual unit should always be more than one person. The persistence of that shame serves as a reminder that our culture war isn't just about who we have sex with, but about why we have it in the first place. Is sex solely about connecting with one other person in intimate relationship, or is it about delighting in something that first and foremost, belongs to us as individuals? One of our most universal and private human pastimes lies at the very heart of the sex wars.