Life is full of delicious ironies, especially if you know where to look for them.

Consider the debate over SB 129, Georgia's proposed "Religious Freedom Restoration Act." At this point, the entire argument is over one sentence recently added to the bill by the House Judiciary Committee. That sentence reads: "Courts have consistently held that government has a fundamental, overriding interest in eradicating discrimination."

As long as that sentence remains in the bill, SB 129 will not give individuals or businesses a religious-based license to discriminate against gay people. If that sentence is removed, SB 129 does give individuals or businesses a religious-based right to discriminate against gay people. That's what the whole fight is all about.

And once again, let's be clear: This is not a relatively minor dispute about whether bakeries can legally refuse to provide a wedding cake to gay couples. Such isolated cases represent only a very tiny opening sliver of a very large wedge that backers of SB 129 are attempting to drive into law. SB 129 is really about whether employers will be able to offer benefits to married straight couples while denying those same benefits to married gay couples on the grounds that they have a religious objection to gay marriage. It's about whether gay employees can be fired simply for being gay or suspected of being gay, again because employers have a religious objection to "the gay lifestyle."

Now, I promised you a delicious irony, and here it is:

One of the arguments most commonly offered by conservatives against gay marriage is that it will inevitably open the door to legalized polygamy. That seems to be a deep-set, heartfelt fear among many on the right. And the inconvenient truth is that if they succeed in passage of SB 129 and other state RFRAs, they will open the door to polygamy much wider than gay marriage ever could.

Why? It comes down to which of two competing legal standards, "rational basis" or "compelling government interest," are applied to the question.

Under the First Amendment, government can't pass laws that are intended to restrict religious liberty. Such laws are not at stake in this discussion. However, state and local laws that accidentally impinge on religious liberty -- zoning laws, health and safety laws, etc., criminal statutes, laws against polygamy -- have been allowed as long as those laws at least have a rational basis.

Under SB 129, however, a mere "rational basis" would no longer be sufficient. Laws that impinge accidentally on religious liberty would be allowed ONLY when those laws advance a "compelling governmental interest."**  In legal terms, the difference between "rational basis" and "compelling governmental interest" is profound.

How does that affect the polygamy case? When proponents of polygamy attempt to defend the practice in courts or other forums, they almost always do so in terms of their religious freedom. To them, it's a First Amendment issue. But so far, state laws against polygamy have been upheld as constitutional because courts have found them to at least meet the "rational basis" test.

However, if a mere "rational basis" is no longer enough thanks to RFRA, you would need a "compelling governmental interest" to continue to outlaw polygamy. And that's where the danger arises.

Peter Nash Swisher, a national expert in family law and a professor at the University of Richmond Law School, has looked at the issue and is very dubious about whether such a compelling interest can be found. With recent Supreme Court decisions combined with state and federal RFRAs, " ... proponents of polygamous marriage now have, in my opinion, a very strong case for validating polygamous marriages on cultural, religious, and constitutional grounds."

As Swisher notes, the Old Testament is full of instances of polygamy, and the Muslim faith allows a man to have as many as four wives. Martin Luther, the founder of Protestantism, "observed that polygamy does not contradict Scripture, and so cannot be prohibited by Christianity."*** The Catholic Church did not outlaw polygamy until 1563, and the Mormon Church did not do so until 1890.  In fact, Mormon leaders abolished polygamy only after a U.S. Supreme Court ruling that allowed the federal government to strip the church of all of its property, including its temples and cemeteries, and to basically abolish the church as a legally recognized entity.****

Such a ruling would be almost inconceivable under modern First Amendment jurisprudence.

The very conservative, evangelical-based Family Research Council has tried to anticipate this legal challenge under RFRA and has laid out its arguments here. But frankly, they're not very convincing. For example, the FRC claims that government would have a compelling interest in banning polygamy because "anthropologists have identified problems in modern polygamous households, such as the fact that 'young girls are often tricked or coerced into marrying older wealthy men and that women and children of modern polygamy are often poorly educated, impoverished, and chronically dependent on welfare'."

Those social problems are significant, but they are hardly unique to polygamy. I'd hate to be the lawyer trying to argue that young girls aren't "tricked or coerced into marrying older wealthy men" under monogamy , for example. In addition, constitutional law requires that the solution to such problems be the "least restrictive possible," and an outright ban on polygamy would not meet that test.

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** That's why the statement in SB 129 that "government has a fundamental, overriding interest in eradicating discrimination" is so important. It states explicitly that preventing discrimination meets the definition of a compelling government interest, and thus would not be overridden by RFRA.

*** Luther wrote: "I confess that I cannot forbid a person to marry several wives, for it does not contradict the Scripture. If a man wishes to marry more than one wife he should be asked whether he is satisfied in his conscience that he may do so in accordance with the word of God. In such a case the civil authority has nothing to do in the matter."

**** One of the named plaintiffs in that Supreme Court case was George Romney, relative of the 2012 Republican presidential candidate.