Several thousand opponents of same-sex marriage march in front of the Supreme Court on April 25. The crowd also attracted a handful of same-sex marriage advocates. (Sarah Pulliam Bailey)

The Supreme Court will begin hearing oral arguments this week on same-sex marriage, a case expected to be divisive across the nation. Even those who oppose same-sex marriage disagree on how to argue the case against it.

As the Supreme Court hears Obergefell v. Hodges this week, attention turns to the oral arguments for and against the state laws defining marriage as being between one man and one woman. The court also can consider the scores of arguments offered in legal briefs filed by “friends of the court.”

Many of the arguments are from religious groups with strong opinions on both sides of the issue. More than a dozen briefs have been filed by religious conservatives concerned with defending traditional family structures.

The briefs reveal deep divisions about basic foundations in the larger case against same-sex marriage. The religious groups are divided, for example, on whether the argument against same-sex marriage is religious.

A number of those who filed briefs think it is important that the case be made in strictly secular terms. The United States Conference of Catholic Bishops, for example, says its argument is based on the facts of nature, not theology.

“It is a mistake to characterize laws defining marriage as the union of one man and one woman as somehow embodying a purely religious viewpoint over against a purely secular one,” the bishops say in their legal brief. “Rather, it is a common sense reflection of the fact that (homosexual) relationships do not result in the birth of children, or establish households where a child will be raised by its birth mother and father.”

The case before the Supreme Court could hinge on whether state laws defining marriage as heterosexual are motivated by animus. If the purpose of the laws is to discriminate against gay men and lesbians, then they can be seen as violating the equal protection clause of the 14th Amendment. If the state has a legitimate public interest in restricting marriage to opposite-sex couples, then bans on same-sex marriage can stand.

According to the bishops, the laws defining marriage as heterosexual do serve a public interest. The laws reinforce beneficial social norms, they say, that only “happen to correspond with religious beliefs.”

Another brief, submitted to the Supreme Court by Texas Values, makes the same argument. “There is nothing ‘religious’ about this perspective on marriage and sexuality,” the brief says. “It is held by many secular individuals and defended in secular terms.”

To defend the states’ marriage laws in secular terms, many religious groups turn to sociological evidence. They argue that same-sex marriage is bad for society or that giving opposite-sex marriage a special status is good for society.

The Family Research Council makes both arguments. The group says, “the legalization of same-sex marriage, through legislation or litigation, inevitably would be detrimental to the institution of marriage, children and society as a whole.” Restricting marriage to heterosexual couples, on the other hand, works to “channel the potential procreative sexual activity of opposite-sex couples into stable relationships in which the children so procreated may be raised by their biological mothers and fathers.”

Ryan T. Anderson, an opponent of same-sex marriage (recently profiled by The Washington Post), makes a similar argument about human flourishing. “Redefining civil marriage,” he tells the court, “will obscure the true nature of marriage and undermine the principled basis of its norms, and, over time, people’s adherence to them.”

Those who oppose arguments about social good of traditional marriage raise questions about the marriages of infertile opposite-sex couples, against children born out of wedlock, against divorce, or even against adoption.

Several religious groups actually take up the case against adoptions by opposite-sex couples as a reason same-sex marriage is not in the interest of the state. The Ruth Institute says that children of same-sex marriages may turn out like adopted children, many of whom are confused and angry, and that this is a reason to oppose such unions. The Family Policy Institute and the Christian Medical Association likewise say that children raised in same-sex households will suffer “geneological bewilderment” of not knowing their biological parents.

Most of the religious groups that oppose same-sex marriage are strong advocates for adoption, though. They are uncomfortable with arguments that imply that adopted children are bad for society regardless of whether their parents are in a same-sex or an opposite-sex marriage.

Many religious groups worry that secular arguments undercut their ability to participate in public debate, telling the court that their arguments actually are religious. It is, in fact, important to them that their arguments are religious. If the court excludes religious rationales, deeming theological motivations irrational, then religious people cannot speak on the moral, social issues they care about so deeply.

One brief, filed by five Christian conservative groups, including the North Carolina Values Coalition and the Christian Family Coalition, warns that the “American judicial system is becoming allergic to religious expression or influence in the public square.”

The groups say that laws defining marriage are always based on people’s religious beliefs — as are all laws. “Every law has a moral foundation and many are based on ‘moral disapproval,’ ” they tell the court. “The question is whose morality will prevail.”

A similar case is made in a brief filed jointly by the National Association of Evangelicals, the Ethics & Religious Liberty Commission of the Southern Baptist, more than a dozen conservative Protestant denominations and the Church of Jesus Christ of Latter-day Saints. These groups argue that their beliefs about marriage are both religious and practical.

“These beliefs,” they say, “are rooted in our theologies and in centuries of one-to-one counseling and personal experience with intact and broken families, functionally fatherless children, and single mothers.”

The line between religious and secular is not so neat for evangelicals in particular. They reject same-sex marriage because they believe that’s what the Bible says. But they also believe the Bible offers the best and most practical guide to human flourishing, so if the Bible condemns homosexuality it is because it is bad for people and society.

“A decision that traditional marriage laws are grounded in animus would demean us and our beliefs,” the brief says. “It would stigmatize us as fools or bigots, akin to racists.”

A large number of the religious organizations that oppose homosexuality made religious concerns the focal point of their briefs to the Supreme Court. According to the legal brief filed by the Texas Eagle Forum and Steven F. Hotze, founder of the Conservative Republicans of Texas, the court’s ruling in this case could even be seen as “rejecting the Bible as false.”

The Texas Eagle Forum and Hotze argue that even apart from the damage done to the nation by same-sex marriage, that ruling is wrong in secular terms because it would “be disastrous for the unity of our Nation.” The ruling would “weaken the strongest link that holds our society together,” a common culture of respect for the Bible.

The justices may or may not take these arguments into consideration. Whichever way the court goes in Obergefell v. Hodges, it will be decisive. The wide range of arguments from religious groups that oppose same-sex marriage shows, though, that even when Americans agree on the definition of marriage, they disagree in deep and fundamental ways.

Daniel Silliman is an instructor of American religion and culture at Heidelberg University and an associate editor of “Religion and the Marketplace in the United States.” You can follow him on Twitter @danielsilliman.

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