Fundamentalist Mormon Joe Darger, along with two of his three wives, recently appeared on O’Reilly to discuss their new book, Love Times Three: Our True Story of a Polygamous Marriage.

O’Reilly began the segment by pointing out that opponents of same-sex marriage have always argued that if marriage was redefined to include same-sex unions, other groups would want the same treatment. This is the classic “slippery slope” argument, and despite arguments to the contrary by leading gay thinkers (such as philosophy professor John Corvino), the slide down this slope appears inevitable.

In 2004, polyamory advocate Jasmine Walston stated, “We’re where the gay rights movement was 30 years ago.” Just five years later, Newsweek featured an article entitled, “Polyamory: The Next Sexual Revolution,” stating, “It’s enough to make any monogamist’s head spin. But the traditionalists had better get used to it.” The story reported that, “Researchers are just beginning to study the phenomenon, but the few who do estimate that openly polyamorous families in the United States number more than half a million, with thriving contingents in nearly every major city.”

Without a doubt, it’s a very short leap from polyamory to polygamy, and just as TV shows like Will and Gracehelped pave the way for a more gay-affirming society, shows like Big Love and Sister Wives are helping to pave the way for a more polygamy-affirming society.

Not surprisingly, in Canada, where same-sex marriage is legal throughout the country, Monique Pongracic-Speier, an advocate with the Canadian Civil Liberties Association, has argued on behalf of polygamists that, “Consenting adults have the right-the Charter protected right-to form the families that they want to form.” If homosexuals can, why can’t polygamists?

The logic really is quite strong: If someone has the “right to marry the person they love,” as gay activists incessantly tell us, why shouldn’t people have the right to marry multiple loving partners?

Following the same logic, when Columbia University professor David Epstein was charged with having a three-year, consensual affair with his adult daughter, his attorney, Matthew Galluzzo, said, “It’s OK for homosexuals to do whatever they want in their own home. How is this so different? We have to figure out why some behavior is tolerated and some is not.”

As Rush Limbaugh noted, students posting on “the Columbia University student newspaper website [were] mystified as to why it’s illegal: ‘Wait, why is consensual incest a crime? It might not be appealing to everyone, but if they’re adults and they consent, who cares what they do?’ This is a typical comment from a student on the site.”

Attorney Galuzzo, cited in the Huffington Post, went as far as to question whether “prosecuting incest was ‘intellectually consistent’ with the repeal of anti-sodomy laws that resulted from Lawrence v. Texas in 2003.” He even asserted that “what goes on between consenting adults in private should not be legislated” because the bedroom “is not the proper domain of our law.”

And in a well-known case in Germany, the attorney of a brother and sister, separated as children but then reunited as adults and in an incestuous relationship for years, has argued for the repeal of incest laws using arguments similar to those that have been advanced in support of same-sex marriage. Time magazine even asked in 2007, “Should incest be legal?”

The slippery slope argument really is quite compelling, and yet there is a fundamental fallacy which is often overlooked in the contemporary debate. Specifically, it is the fallacy that polygamy is further down the slope than same-sex marriage. Actually, the reverse is true, even if it may not be chronologically true in America.

Simply stated, throughout human history, the essential components of marriage have always been a man and a woman, not merely two people. This means that polygamy represents a less radical redefinition of marriage than does same-sex marriage, since polygamy includes the essential components of male and female.

And, even though the vast majority of Americans are fundamentally opposed to polygamy (for good reason), it has been practiced throughout history and it remains common in many countries today. Polygamy is even found in the Bible, although it is consistently painted in a negative light and the ideal set forth in the Scriptures is the lifelong union of one man and one woman. In short, polygamy is a serious distortion of the divine ideal, whereas same-sex marriage, from a scriptural viewpoint, is a complete perversion of that ideal.

The offshoot of all this is simple: If we don’t have the wisdom and the will to resist the radical, gay redefinition of marriage, we will certainly not be able to resist the movement towards polygamy.

It’s time to wake up, America. We are further down the slippery slope than we realize, and we can’t afford to lose any more ground.