I cite as just the latest evidence John Pomfret's Washington Post article, " Polygamists fight to decriminalize bigamy." Pomfret cites multiple ways in which the gay marriage and polygamous marriage movements are closely tied – whether the former want it or not:
Consciously taking tactics from the gay-rights movement, polygamists have reframed their struggle, choosing in interviews to de-emphasize their religious beliefs and focus on their desire to live "in freedom."
The U.S. Supreme Court's 2003 decision in Lawrence v. Texas, which voided laws criminalizing sodomy, also aided polygamy's cause because it implied that the court disapproved of laws that reach into the bedroom.
Jonathan Turley, a law professor at George Washington University … has written two op-eds for USA Today calling for the legalization of bigamy -- and same-sex marriage. "I find polygamy an offensive practice," said Turley, who has become something of a celebrity among polygamists in Utah. "But there is no way its practice among consenting adults should be a felony."
Turley is right – the political movement to let consenting adults marry any way they want to is a potent one. The action in polygamy prosecution has shifted recently as a result of these new political realities. Even the Attorney General of Utah, who is on the front line of this struggle, has publicly announced that he will not enforce the state's bigamy laws. Instead, he only goes after polygamists for rape, incest, and welfare fraud – as he would with non-polygamists, too.
Proponents of gay marriage are usually liberal. Proponents of polygamy are usually conservative. If they had their way, they might each write the law to include their kind of marriage and exclude the other kind. But the political movement they are both riding – marriage is a private choice of individuals that society should just accept – is a tiger they are holding by the tail. If they don't let go, the tiger will eat both movements, and much more beside. And then we will have no marriage at all. Only whatever private contracts any consenting adults want to make.