American common law definitions of marriage were historically shaped by the influence of Christianity. In God's Joust, God's Justice: Law and Religion in the Western Tradition, John Witte Jr. does an excellent job of explaining the formation of marriage law, writing that what defined marriage for centuries in the West was its emphasis on procreation and fidelity, and the institution's sanctity, civil use in curbing vices and establishing the foundation for education, and usefulness in maturing a couple's Christian faith. This understanding no longer exists in our culture, and some argue that when Americans began divorcing in high numbers, redefined marital sexuality via contraception use, and reduced marriage to mere commitment, it set the stage for our current same-sex marriage debate.
Because church-going evangelicals divorce at high rates, this community of believers has lost its moral authority to defend the indissolvable nature of marriage. For example, I recently gave a lecture at New York University explaining the traditional view of marriage and was asked: "Then why is the divorce rate among conservative Christians so high?" It was a great question. I wish the divorce rate for believers was 0 percent. I couldn't say much in defense. It seems that many Christians have forgotten that the Lord hates divorce (Malachi 2:16).
Because of the work of Howard Kainz, professor emeritus at Marquette University, many argue that married couples using contraception redefine sex in ways that render same-sex marriage unobjectionable. Kainz observes:
"[I]f you believe you have a right to non-procreative sexual intercourse, you have no right to criticize non-procreative sex by others-for example, by a gay couple. You may justify your personal practices on the basis of your genuine mutual love and commitment to lifelong fidelity. But homosexuals may be even more intensely in love with each other and even more firmly committed to mutual fidelity. They may even be more open to procreation than you are, through adoption or through in vitro fertilization. To want to have sex without the possibility of offspring, and condemn others for similarly non-procreative sex, would be blatantly inconsistent."
Because of the sex/children connection, George Mason School of Law professor Helen Alvaré explains in two articles why American marriage historically did not divorce itself from children.
Lastly, the reduction of marriage to a mere contract between consenting adults has stripped marriage of its sanctity and its family-forming utility in shaping the common good, as John Calvin would encourage.
As a result, I'm beginning to wonder if the alternative marriage debate is not already lost. Christians do not provide a model of marriage in practice that makes a persuasive case against changing the traditional definition. A theologian friend says that the marriage debate in America is doomed unless it is defined as "a sexuality-based social institution for the union of the couple and the procreation and nurture of children." Otherwise, marriage will continue to be defined by utilitarian moral relativists.