In a game-changer for the legal fight over same-sex marriage that gives credence to opponents’ “slippery slope” arguments, a federal judge has now ruled that the legal reasoning for same-sex marriage means that laws against polygamy are likewise unconstitutional.

In his 91-page opinion in Brown v. Buhman, on Dec. 13, U.S. District Judge Clark Waddoups struck down Utah’s law making polygamy a crime. In so doing, he may have opened Pandora’s Box.

As a condition for becoming a state in 1896, Congress required Utah to outlaw polygamy, which is marriage between three or more persons. This case involved a family of fundamentalist offshoots of nineteenth-century Mormonism. The Church of Jesus Christ of Latter-Day Saints disavowed polygamy in 1890, and again in 1904, but some splinter groups continue the practice.

Waddoups’ opinion would not only cover such groups, however, but also Muslims or anyone else who claims a right–religious or otherwise–to have multiple-person marriages. He notes that the Supreme Court ruled against polygamy in its 1878 case Reynolds v. U.S., but said he cannot simply rest upon that decision “without seriously addressing the much developed constitutional jurisprudence that now protects individuals from the criminal consequences intended by legislatures to apply to certain personal choices.”

In its 2003 Lawrence v. Texas case, the Supreme Court overruled previous sexuality precedents by declaring unconstitutional laws that made homosexual sodomy a crime, holding that although the Constitution says nothing about sex or marriage, there is nonetheless a right to consensual sexual activity between adults that government cannot regulate. This was over the vigorous dissent of conservative justices, who said that the Constitution commits such questions of marriage and morality to the states and the democratic process, and that therefore federal courts have no power to impose their own moral judgments.

The Lawrence case lays the foundation that has been cited for a decade now in court to make the case for a constitutional right to same-sex marriage. If government cannot forbid homosexual conduct, this argument goes, then neither can it deny those who define themselves by homosexual behavior to officially recognize any such relationship as a marriage. It began a political, religious, and philosophical debate in America between two different definitions of marriage and family.

For over 5,000 years of recorded human history, marriage laws worldwide were about providing a social structure for producing and raising children. These laws simply acknowledged the biological reality that only sex between a man and a woman can produce a baby, and that, correspondingly, that every child born into the world has two parents, one of which is a man, the other a woman.

Marriage laws were designed to secure parental rights for that man and woman over the child they had created, and also imposed strict duties and obligations on each of them for raising that child. As part of that, those laws also bound the man and woman to each other, imposing obligations of sexually exclusivity, mutual care, and support.

Those laws were created for the nurturing of those children, and assign the gender role of demanding the man’s protection and support of the woman during pregnancy and once the children were born. They were designed primarily for the protection of children, and secondarily for the support of women.

A man and woman would form a new family to act as a single unit in society, and care for any children resulting from their monogamous sexual relationship. Thus, marriage has been defined as the union of one man and one woman. More precisely, it is the union of (1) two consenting persons, (2) of opposite biological sex, (3) who are not close blood relatives.

The new conception of marriage, rooted in the proliferation of no-fault divorce laws in the 1970s and the sexual revolution, is that marriage is about personal happiness and fulfillment. People should be free to form whatever relationships they find personally satisfying and to follow whatever their personal sexual inclinations are to engage in whatever form of sexual behavior they find gratifying.

If, therefore, you have a right to officially recognize those homosexual relationships through redefining marriage to include same-sex couples, then there is no reason to say it cannot include more than two people, so long as everyone is a consenting adult.

This lawsuit is the brainchild of Prof. Jonathan Turley at George Washington University. He’s designed a two-step strategy, piggybacking on same-sex marriage: first, decriminalize polygamy, then assert a right to official recognition of polygamy.

As Turley explained in previous court filings, he believes there is a “right to self-determination of private relations and family matters free of government intrusion.” He noted that many oppose polygamy, and goes on to assert that polygamists “are entitled to protection from such majoritarian animus and bias vis-à-vis their private lifestyles and relations. Their status under domestic law is a civil rights issue deserving the same protections afforded to homosexuals and other minority groups.”

The exact legal arguments for same-sex marriage equally apply to multiple-person marriages. Turley acknowledges that marriage laws that do not include both are “a tool for the imposition of a uniform moral agenda or tenets on citizens.”

Turley then goes on to make clear he is not only arguing for the form of polygamy technically called polygyny, which is one man with multiple women. In other words, he also argues for a right to polyandry (one woman with multiple men) and polyamory (multiple men with multiple women).

Waddoups concluded that Reynolds has been overtaken by Lawrence and other recent legal developments. While keeping in place for now the Utah law against issuing multiple marriage certificates for polygamous marriage (the second step of the Turley strategy), he invalidated the criminal law against multiple adults cohabiting together as a family, which is the core of the laws against polygamy.

This case will likely now go to the U.S. Court of Appeals for the Tenth Circuit in Denver.

Ken Klukowski is senior legal analyst for Breitbart News. Follow him on Twitter @kenklukowski.