The ongoing case of Perry v. Schwarzenegger is about whether California voters have the right to exclude gays from the institution of marriage. Yet this case about gay rights could inadvertently sweep aside any rational defense against polygamy. The reason is that the state’s justifications for excluding polygamists from the institution of marriage in Reynolds v. United States, the 1888 ruling that confirmed polygamy’s unlawfulness, are under attack.

This is not an article attacking the idea of gay marriage. As a conservative I strongly support gay marriage because two loving parents are, on average, better than one and the more people who join the bourgeois institution of marriage, the more people are voting Republican as married upper-middle class consumers with kids.

That doesn’t mean that the legal consequences of declaring a right to marriage should be overlooked.

In Perry v. Schwarzenegger the state has the burden to prove a rational basis for excluding homosexuals from the institution of marriage. The court case is a direct result of California voters passing Proposition 8 in 2008, which limited marriage to one man and one woman.

Arguments that it would be harmful to children or undermine the institution lack supporting evidence. Marriages occur all the time between straight couples who cannot procreate, who are abusive or who have no religious basis for their marriage. No negative repercussions have been linked between gays marrying and the broader society.

Even if a rational basis were found it may not be enough if the courts determine that marriage is a fundamental right or a minority is being treated differently with a suspect classification (such as race or religion). In that case the state would have to prove their concerns are not just rational but essential for the institution of marriage (known as the “strict scrutiny standard”).

Using all of these arguments practitioners of polygamy would have a powerful case. Like gay marriage, polygamy is based on consent between loving adults and does not run afoul of any consent issues more than traditional marriage. While the vast majority of people may oppose legalizing polygamy, that alone is not a reason to keep it illegal. Most people opposed interracial marriage when the case of Loving v. Virginia ruled laws against miscegenation violated the constitution.

Opponents could argue that marriage is designed for two people rather than three or more, but this is suspect for several reasons. One is that for hundreds of years it was a man and a woman, and that failed the test. The other is that Reynolds actually addresses the traditional history of polygamy (which has been much more common of a family structure than gay marriage throughout history) and dismisses it as “almost exclusively a feature of the life of Asiatic and of African people.” Reynolds also talks about marriage as the foundation of society and the damage caused by polygamy, but does not rely on any studies or scientific data.

If marriage is found to be a fundamental right or even a right that requires a rational basis, the march to the legalization of bigamy or polygamy may be here sooner than we think. After all, if two gay men down the street don’t affect my marriage, why would a union of two women and one man?