Marriage is great, the joke goes, if you like living in an institution. The quip’s humor, and its grain of truth, relies on the uneasy juxtaposition of love on the one hand and law on the other. Lulled by the thought of happy coupledom, the listener is brought up short by the image of the state.

It is precisely this dual function of modern marriage–to bestow civil rights and to declare publicly a private sentiment–that makes its expansion to same-sex couples so deeply contentious: It is the ultimate act of assimilating gays and lesbians into both the apparatus of the state and the mainstream culture’s imagination of intimacy. As such, the push for same-sex marriage represents a marked departure for the gay rights movement from its outsider origins in the drag queen riots of Stonewall and the more anarchic, free-love celebration of the 1970s.

For better or worse, gay activism over the last 15 to 20 years has focused not on the overthrow of the institutions of straight society, but on the fight to enter them. And not just any institutions, but the two that lie at the symbolic core of the modern nation state: the military and the family. Despite the right’s best efforts, political contests no longer pivot on sex (the kernel of gay people’s difference), but on civic participation (the basis of their sameness).

This shift in the rhetorical center of gravity has brought with it a raging debate on the societal effects of allowing same-sex couples to marry. The religious right contends it will knock the last strut out from under the besieged institution, and damage children in the bargain. Gay rights advocates call that nonsense and argue that to deny same-sex couples the right to marry relegates them to the status of second-class citizens.

What’s been lacking up to this point is much empirical evidence as to what these supposed effects on society might be–a gap that M.V. Lee Badgett’s compellingly argued new book, When Gay People Get Married, seeks to fill. Her premise is simple: If we want to measure the consequences of same-sex marriage, then let’s examine a country that already permits it, in this case, the Netherlands. Through interviews and statistical analysis, Badgett, an economist at the University of Massachusetts, aims to show that, in fact, allowing same-sex couples to marry has no deleterious consequences for society and that, moreover, it is gay men and lesbians who will be changed by participating in the institution, not vice versa.

One could be forgiven for wondering why such obvious conclusions need much empirical support. The right’s framing of the debate as a “defense of marriage” has always had a kind of hysterical illogic to it. As Elizabeth Birch, the former head of the Human Rights Campaign, once asked then-Representative Bob Barr, “Which marriage are you defending? Your first, your second, or your third?” The idea that gay people could do any more damage to the sanctity of marriage than straights already have seems, frankly, a little preposterous.

But as Badgett suggests, high-handed dismissal won’t get you far in politics. Given the much higher rate of approval for same-sex marriage among young Americans compared with their parents and particularly their grandparents, right wingers are fighting a rearguard action, one that 50 years hence is likely to be viewed with the same bewilderment as opposition to interracial marriage is now. But at the moment, as recent electoral and legislative defeats for same-sex marriage in California, Maine, New York, and New Jersey show, they are fighting rather well. In this context, a study like Badgett’s, which does such a careful job of marshaling data and refuting the sky-is-falling predictions of conservative social critics, is a very useful resource for advancing a policy discussion based on evidence rather than fear.

In 2001, Holland became the first country in the world to offer full civil marriage to same-sex couples, granting them the legal rights along with the word itself. Two years later, Badgett spent a year living in Amsterdam studying the effects of this watershed change. Her results are drawn from two sources, a qualitative analysis of interviews with 19 lesbian and gay couples about their attitudes toward and experience of marriage and a quantitative analysis of larger patterns in the statistical data on European and American family life.

Badgett’s Dutch couples say they got married for the same reasons most heterosexuals do: to make a public expression of love and commitment, because they’re considering having children or buying a house, or simply because it’s the romantic thing to do. With an 80 percent approval of same-sex marriage rights in the Netherlands, they meet not only with broad acceptance, but reinforcement of public expectations from family and colleagues. We hear the story of a lesbian browbeaten into marriage by her grandfather, and another corrected by a co-worker when she refers to her spouse as her girlfriend rather than her wife.

Interestingly, gay couples in Holland have thus far registered or married at a lower rate (22 percent) than in Massachusetts and Vermont, where the figure approaches 50 percent. This parallels higher overall marriage rates in the United States, where, unlike Europe, health care is often tied to a spouse’s job, and where co-habitants have no formal legal rights in the event of dissolution, as they do in the Netherlands. Social democracies, by providing a stronger safety net, decrease the economic incentives for marriage; their marriage rate is lower, but then so is their divorce rate.

Overall, what Badgett finds is that lesbians and gay men are fitting into the existing model of marriage in the Netherlands rather than reinventing the form. Of course, to marry is still a more political act for them than it could ever be for different-sex couples and will likely remain so for years to come. But, Badgett writes, “[w]hat marriage means to heterosexuals has already changed, and its current form is a good fit for the interests of gay men and lesbians.” “I want to be able to stand up…just like my brother, just like my sister did and say, ‘This is the gal,’” one of Badgett’s female interviewees tells her. “In my family, it’s kind of an important thing to be able to do.”

Badgett’s interview study, though not as diverse in its sample as one might wish given its heavy representation of well-educated, urban, middle-aged women, does gives social science confirmation to an intuitive and anecdotal truth. Marriage–and here I am talking about the word itself–means more than legal entitlements. In courts and legislatures, gay-rights advocates often describe marriage as a bundle of rights that, better than any other status one might create, ties a couple and their families together. Less often described is the way in which the word performs this same task on the social level. Badgett’s couples report that once they married, their friends and families had a much easier time not only accepting their relationships, but interpreting them. Which is to say that the word “marriage” cuts through a great deal of ambiguity in the myriad forms modern relationships take; it provides social clarity, both for the couples and society. This benefit is clearly one of the reasons that gay couples in the Netherlands who do decide to formalize their relationships overwhelmingly prefer marriage to the nearly identical registered partnerships still available to them.

Even the lesbian feminists Badgett encounters who view marriage as an outdated and patriarchal institution of which they want no part seem to understand its appeal. “The commitment and the public commitment, I think–there is something beautiful about it,” one of them says. “I won’t deny that.”

Such is the expressive power of the institution for both gays and straights. And it is this aspect of marriage–its social signaling–that becomes all the more important in a culture where marriage is no longer a near-universal obligation to achieve adulthood but rather a personal choice expressive of one’s own values and commitments. This is precisely why the fight over same-sex marriage in the United States is so intense. To allow it is to grant that gay people are, above all, ordinary. And for some conservatives that heralds a kind of social Armageddon.

But why should it? Does the expansion of marriage rights to same-sex couples have a demonstrably negative impact on society’s fabric? This is what Badgett sets out to answer in the first quantitative chapters of the book, where she takes on Stanley Kurtz of National Review and others who have tried to use demographic data from Scandinavia and the Netherlands as dire warnings of what is to come if we let women marry women and men marry men. The gravamen of their argument is that marriage is dying out in Northern Europe, leading to more and more out-of-wedlock births, and that same-sex partnership rights are a leading cause of the problem because they sever the historical relationship between marriage and parenthood.

As with any argument over cause and effect, timing is key. Take, for example, the case of Denmark, the first Scandinavian country to offer full civil partnership rights for gays and lesbians, back in 1989. Three statistics graphed from 1960 to the present–the marriage rate, the divorce rate, and the percentage of children born out of wedlock–offer an evolving picture of Danish family life. The marriage rate in Denmark peaked in the mid-’60s, declined through the ’70s, reached its nadir in the early ’80s, then began rising slightly for the next 20 years. Concomitantly, the rate of divorce rose sharply in the 1970s, remained high for 20 years, and then declined slightly through the 1990s. Following this same curve, out-of-wedlock births rose sharply beginning in 1970, peaked around 1990, and have leveled off since. Clearly, then, a law introduced in 1989 can hardly be credited with causing the decline of the traditional family in Denmark.

Having examined similar data for all Scandinavian countries as well as the Netherlands, Badgett concludes that “overall, the most basic elements of the sky-is-falling argument fail these simple tests of plausibility.” She adds, “The only reason that some countries had high rates of unmarried cohabitation and nonmarital births after gay couples won rights is that those countries had high rates long before gay marriage or registered partnership was a politically viable prospect. In fact, the same marriage trends are evident in countries without legal recognition of same-sex couples, kicking gay marriage off the list of possible causes for changing heterosexual marriage and fertility patterns.” What Badgett’s elucidation demonstrates is a fact that should be obvious to even the amateur historian: Changes in traditional marriage and the place of women in society are the preconditions, rather than the results, of the expansion of gay rights. It was the legalization of contraception that broke the necessary relationship between marriage and parenthood, and the adoption of no-fault divorce laws that made the decision about whether to remain in a marriage less about the fear of shame and more about personal fulfillment. Same-sex marriage is the apotheosis of this logic of free choice, not its origin.

But opposing these more profound changes–the impact of which dwarfs that of same-sex marriage–is no longer politically viable on the national stage. Which is the reason that the “defense of marriage” functions as such a useful rallying cry for the right: It channels a much broader anti-feminist sentiment onto a social group that remains fair game for explicit attack on moral grounds. Thus, the Family Research Council argues against same-sex marriage as “unnatural” in the same breath as it decries the advent of “the sexual revolution,” a convenient code phrase for women’s ability to enjoy sex without getting pregnant.

Having calmly eviscerated the conservatives’ doomsday arguments regarding Northern Europe, Badgett devotes her book’s penultimate chapter to sorting through what the developments in Scandinavia and the Netherlands portend for the United States. Aggregating the European data, she concludes, “High levels of tolerance [for gay people] and [heterosexual] cohabitation appear to be necessary conditions for country-level change, with low levels of religiosity and a national level of commitment to social spending (on housing, old age, survivors, health, families, employment, unemployment, and income support) adding greatly to the movement toward change.” Thus, even Spain, the third country to offer full marriage to gay people on a national basis, and which has a more religious population, saw increasing rates of cohabitation in the 1990s and the extension of partnership laws by several local governments before the national law was passed in 2005. (The obvious exception to this rule is South Africa, where a broad non-discrimination clause including sexual orientation and gender was written into the constitution, and a subsequent ruling by the Supreme Court made explicit that this protection against discrimination extended to the right to marry.)

Applied to the state-by-state developments in the United States, Badgett’s resulting prediction is unsurprising. In the years ahead, the states most likely to join those already offering either domestic partnership rights or same-sex marriage are places like Maryland, Delaware, Rhode Island, Wisconsin, or Colorado, which already have relatively high levels of gay visibility, social tolerance, and higher-than-average levels of unmarried heterosexual cohabitation.

In October of last year, President Obama gave the keynote address at the Human Rights Campaign’s annual dinner, where he made a number of specific pledges to an audience frustrated by what they saw as his administration’s inaction on gay rights. He would sign the anti-gay-hate-crimes bill recently passed by the House as well as the Employment Non-Discrimination Act if and when it reached his desk; he would end “Don’t Ask, Don’t Tell”; and he would support the repeal of what he described as “the so-called Defense of Marriage Act.”

To no one’s surprise, what he did not do was reverse his stated opposition to same-sex marriage itself. Of course, very few people in the audience believed that Obama was actually against the idea, anymore than they believed Hillary Clinton was against it in the primaries. In the Kabuki theater of American gay politics, gays and lesbians read the stylized demurrals on gay marriage as obeisance to electoral necessity. What such positions lack in integrity, they make up for in being untrue.

Gay organizations have been more vocal than most at pressuring Obama from the left during his first year in office, protesting a fundraiser and loudly calling him out for dragging his feet on his campaign promises. Which is one of the reasons he was at the HRC dinner in the first place. The groups have at the very least succeeded in getting his attention, and in Washington that can make all the difference.

But if that’s the best he can do, advocates had best look elsewhere for real progress. And indeed, they have. On the legal front, there are now two cases in federal court seeking a ruling in favor of same-sex marriage–one challenging Proposition 8 in California, the other challenging the clause in the Defense of Marriage Act that says the federal government shall ignore same sex marriages in states which already permit them. The first of these cases is controversial within the movement; many gay rights groups fear the Supreme Court is not ready to establish same sex marriage as a constitutional right, particularly in the current political climate. The battle for marriage rights in the states will, meanwhile, continue with efforts to overturn Proposition 8 at the ballot box and keep up legislative pressure in states like New York and New Jersey. And focusing on the states is not the same as lowering one’s expectations. Badgett’s book suggests that, whatever the short-term setbacks in places like California or Maine, the larger social trends in the more liberal states will eventually lead to adoption of same-sex marriage, which could eventually push more moderate and even conservative states toward reconsideration. And in the wake of recent defeats, it’s important to remember that ten years ago it would have seemed preposterous to predict gay people would be permitted to marry in states like Iowa and New Hampshire, and yet today they are.

In the meantime, in addition to providing the most solid empirical case to date on why supporters of the institution of marriage have nothing to fear from expanding it to include same-sex couples, When Gay People Get Married might also serve to remind both marriage advocates and their progressive allies that marriage equality for gays and lesbians is not, in the end, a matter of single-issue politics. In the longer view, feminism, a healthy social safety net, and same-sex marriage rights should be understood as fights in the same struggle. They are all efforts to expand human freedom and grant all individuals a legal and social context in which to flourish. To advance one is to advance the others. The utopians of the 1970s may have been replaced by Washington lobbying groups, but that is no reason that old allies shouldn’t find common cause again.