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.