After the Supreme Court’s landmark gay marriage decision, can a constitutional right to plural marriage be far behind? It seemed that way in 2013, when a federal district court in Utah followed the Supreme Court ruling by striking down part of the state’s bigamy law in a case involving the family featured in the television show Sister Wives.

But on Monday a federal appeals court reversed the decision.

It said that the case was moot because Utah prosecutors had shelved prosecution of the Sister Wives family and announced a new policy to prosecute polygamists only if they were also suspected of fraud or abuse.

The decision is a sign that the federal courts would like polygamy prosecutions to go away on their own without having to declare a fundamental constitutional right to marry more than one person.

The plaintiffs in the original case are Kody Brown; his legal wife, Meri Brown; and their three “sister wives”, Janelle Brown, Christine Brown and Robyn Sullivan. All belong to the Apostolic United Brethren Church, a group that accepts the Book of Mormon and Joseph Smith’s prophecy, including his encouragement of plural marriage.

Among Mormon fundamentalist groups, the AUB is relatively moderate. Its members interact with their neighbours and do not typically live in communes dominated by a single charismatic leader. The church considers the mainstream Church of Jesus Christ of Latter-day Saints to be fulfilling a divine mission to spread Mormonism, unlike some Mormon fundamentalist groups that oppose it.

The day after the Sister Wives premiere aired in 2010, the police department of Lehi, Utah, announced in response to pressure that it was investigating the Browns for violating the state’s anti-bigamy law.

Utah County Attorney Jeffrey Buhman subsequently announced he was considering a prosecution — a position he stuck to even after the Browns moved to Nevada.

The Browns, represented by Jonathan Turley, of George Washington University School of Law, went to federal court seeking a declaration that the bigamy law was unconstitutional. Before the court could rule, Buhman announced in a sworn court affidavit that he had adopted a new, formal policy regarding prosecution under the statute. Under the policy, his office would prosecute bigamy only if the victim was “induced to marry through their partner’s fraud, misrepresentation or omission”, or if the person charged was “also engaged in some type of abuse, violence or fraud”. The Browns were not suspected of fraud or abuse, so, Buhman said, he did not intend to prosecute them.

Nevertheless, the district court ruled on the Browns’ claim, holding that the Utah bigamy law violated the constitutional guarantees of free exercise of religion and due process.

In its opinion, reversing that ruling this week, a panel of the United States Court of Appeals for the Tenth Circuit declared that the Browns’ case was moot before the district court decided it, because the announced policy did not cover the Browns and the prosecutor had said he wouldn’t charge them.

The opinion was written by Judge Scott Matheson Jr, a member of Utah’s political-legal aristocracy. Matheson’s father was governor of the state and his brother is a congressman. Matheson, a Rhodes scholar, Yale Law School graduate and former US Attorney, was a Democratic candidate for governor in 2004 and was appointed to the bench by president Barack Obama in 2009. Matheson’s fascinating background matters because he combines impeccable, liberal legal credentials with deep connections to Utah’s mostly Mormon political elite. Matheson’s reasoning was simple but not completely convincing. The constitutional idea behind the doctrine of “mootness” is that, under Article III Section 2 of the Constitution, the judicial power extends only to “cases” or “controversies”.

According to the traditional, judicial interpretation of the clause, a case or controversy exists only if there is a live case between two adversarial parties. You can’t challenge the constitutionality of a law unless you have a stake in it. And you can’t ordinarily challenge a criminal law unless you’ve been charged with a crime, or are engaged in conduct that makes it probable that you will be charged.

But, of course, the Browns could still be charged under the county policy if Buhman or another prosecutor came to think that they were engaged in fraud or abuse. Given that an investigation had originally been announced, it’s reasonable to think that the danger of prosecution lingered, which would surely be enough to make the case live.

The court could certainly have gone the other way. A logical conclusion is that Matheson and the other judges wanted to avoid declaring a fundamental right to plural marriage. Not only would such a decision be controversial nationally, it would also be controversial in Utah, where the mainstream Mormon Church has spent a century disentangling itself from the legacy of polygamy.

The court’s goal is surely for polygamy prosecutions to disappear on their own, without judicial intervention. That’s a nice aspiration. But it is unlikely to happen so long as prosecutors want to keep the statute handy for prosecuting polygamists perceived as abusive or fraudulent. Some day, the courts are going to decide whether there is a fundamental right to marry as many people as you like.

• Noah Feldman, a Bloomberg View columnist, is a professor of constitutional and international law at Harvard University and the author of six books, most recently Cool War: The Future of Global Competition