Since same-sex marriage emerged as an issue in the early 1990s, brilliant conservative thinkers have constructed a remarkable series of arguments against it. There are sociological, anthropological, biological, psychological, teleological, and hermeneutical arguments. What unites all these arguments is an underlying belief that certain limits must be placed on human behavior for society to function and for people to lead productive and meaningful lives. This is what traditionalism is.

Proponents of gay marriage have a much simpler argument: Two consenting adults should be free to do whatever they want. The core belief here is libertarian—that it is a fundamental injustice to place limits on human conduct. If homosexuals wish to marry, then marry they should. If “marriage” has always been limited to the joining of a man and a woman, then its definition should change because such a limit is unfair.

The simplicity of the argument is its greatest strength. And what the progress of the gay-marriage debate reveals is that we are all libertarians now—but within limits, of course. For example, Barack Obama has come out as a libertarian on gay marriage, but is very nearly the opposite of a libertarian when it comes to economic matters. Many of those who wept and celebrated on May 9 when the president announced he was a supporter of gay marriage have not blinked an eye as states and municipalities have limited the rights of smokers and property owners, for example.

The growing libertarianism of the United States is the reason a change in law opposed by 80 percent of the public 15 years ago is now a 50-50 proposition—or at least as far as polling goes. And it’s why the endorsement of gay marriage by the president of the United States is far more a reflection of that sea change in attitudes than a sea change in itself. Everybody knew Obama was lying in 2008 when he said he was opposed to gay marriage. He was given a pass by gay advocates because they knew he was on their side and they also knew open advocacy of their cause might harm his bid for the presidency. Now, for reasons that surely include the need to loosen some purse strings he found surprisingly hard to open this year, Obama has stopped lying for political gain and instead has told the truth for political gain.

Which is not to say he did something risk-free. His remarks came the day after voters in North Carolina went to the polls and, in a landslide vote, affirmed the traditional definition of marriage. Which is what always happens, it appears, when voters are asked to express an opinion at the polls. “There have been 31 statewide ballot initiatives on same-sex marriage since 1998,” writes Rod Dreher. “And proponents have lost every single time. Every. Single. Time.”

Traditionalists argue that these public referenda suggest the tide can be turned and the growing acceptance of same-sex marriage can be reversed. But there is a reason that the tide has been flowing in the direction it has, a reason why there has been so little resistance to the growing moral libertarianism of the American people. And that is the crisis within traditionalism itself. Faith traditions and august institutions that had been designed to uphold the age-old pillars of society grew besotted with the possibilities of wholesale social change. By confusing their own fashionable politics with timeless truths, they ceased speaking with authority.

So, yes, marriage will be redefined. And this is the greatest irony of all. The gay-rights movement has been dedicated to “liberation.” But marriage is defined by the limits it sets on your personal freedom. You pledge to be faithful, which limits your sexual freedom. You promise to take care of someone else, which limits your freedom of mobility. You form a unit with someone else, which limits your economic freedom. And you are legally obliged to take fiscal, emotional, and legal responsibility for the children you have together for nearly two decades.

Marriage knits two people into a web of obligation that grows tighter, more complex, and more limiting over time. You surrender freedom. What you get in exchange is richness, depth, transcendental meaning. Which raises the question: Can a liberation movement give up liberation as an end in itself?