Marriage equality opponents are having a hard time pointing to any good reason for fencing same-sex couples out of marriage. So the latest move has been to invite the Supreme Court to cast their collective gaze into the future.

Obergefell v. Hodges, the marriage case before the Court, hears arguments tomorrow morning. Michigan, Ohio, Tennessee and Kentucky want the Court to look into a crystal ball and imagine that a ruling for marriage equality will lead to the erosion of marriage, an increase in single parenthood, and even, according to a group that styles itself “100 Scholars of Marriage,” a dramatic spike in the number of abortions. But the couples challenging the laws insist the Court look at them and at the many other families affected by the law’s refusal to grant them the rights and obligations—and the dignity—marriage creates. Expect the Court to side with those experiencing real problems in the here and now.

As usual, all eyes and ears will be laser-focused on Justice Anthony Kennedy, who sits at the Court’s fulcrum, and who has written all the major gay rights decisions over the past two decades. He’ll have no shortage of information to weigh, as the two sides have assembled all their troops: about one hundred and fifty amicus (friend of the court) briefs have been filed, representing virtually every division of the social sciences; every legal perspective; local, state, and federal politicians; the medical and public health communities; religious organizations; and a clutch of outliers (including “ex-gays,” adult children raised by same-sex parents but who now don’t think their parents should be able to marry, former professional football players and so on).

All those dead trees and stressed servers notwithstanding, the legal arguments for the couples who want to marry (or to have their out-of-state marriages recognized by their home state) are clear, and have been stated many times. In brief: the guarantee of equal protection under the law requires the state to recognize their relationship, unless there is a good reason not to do so. Conversely, non-recognition causes serious harm to the couples and to their families. Plaintiff James Obergefell presents perhaps the most sympathetic case of all: He can’t even get himself listed on the death certificate of his deceased husband, John Arthur, because his home state of Ohio won’t recognize the couple’s out-of-state marriage. Among the other plaintiffs are Valerie Tanco and Sophy Jesty, who can’t get on a single health insurance plan in Tennessee. More worrying, Jesty’s legal relationship to their child is unclear.

Against these realities stand a couple of arguments that the states have been making during the past decade, but that have mostly melted away after a decade that has seen the national dialogue around marriage equality dramatically transformed.

The first argument—that kids do best when raised by a mother and a father—isn’t supported by the evidence. The studies that had reached that conclusion compared intact families to several kinds of families: those headed by single parents; or by a biological parent and a stepparent; or by divorced parents. But the studies didn’t compare kids raised in intact opposite-sex homes to those raised in similar homes headed by same-sex couples. (The few that did have been roundly rejected as methodologically unsound.) As the brief filed by the American Sociological Association makes clear, when the correct comparison is made, children raised by same-sex parents fare just as well as those raised by the opposite-sex counterparts. The telltale sign that the argument is settled comes from an opposing amicus brief from an organization called “the Institute for Marriage and Public Policy,” which urges the Supreme Court to simply ignore all the studies. That’s at best a holding action—professing that we still don’t know enough. The states themselves don’t put up much of a struggle on this issue.

The second argument is that marriage is about procreation and that excluding gays is necessary to protect the only relationship—a man and a woman—that can lead to “natural” procreation. This argument has been thoroughly eviscerated. As Justice Elena Kagan pointed out during oral argument in the Proposition 8 case in 2013, there’s no age limit on marriage—a limit that one would expect if marriage were really all about procreation.

With this wispy underbrush swept away, the focus naturally turns to the many costs imposed by the marriage bans. They’re expensive, because marriage carries many benefits. They’re damaging to emotional and physical health, because, as the brief co-authored by the American Psychological Association points out, excluding same-sex couples from the protection of the law creates a stigma—and stigmatized groups suffer stress, with resulting health consequences. When these barriers are lifted, things improve. A brief from the American Public Health Association contains this striking example: in the year after marriage equality came to Massachusetts, gay and bisexual men enjoyed improved health, as measured by number of health care visits and costs.

The denial of marriage rights doesn’t just harm individuals; these laws needlessly punish dedicated parents and their children. In one stark example from Michigan, a lesbian couple adopted two children with special needs—but because only married couples can jointly adopt in that state, each woman adopted only one of the children. It’s hard to see how this kind of deliberately fractured family serves any societal goal. The legal and social costs of exclusion clearly trouble Justice Kennedy, who expressed concern in United States v. Windsor about how these laws deny the couples dignity, and “humiliate” their children.

In states that have already moved to full equality, the legal and dignitary harms endured by the Obergefell v. Hodges plaintiffs have been solved. Marriage equality isn’t causing grievous harms—quite the opposite. Without any legitimate current damages to highlight, opponents of marriage equality are left arguing that the Court must look still further into the future.

The argument begins by casting the crucial issue not as the problems facing same-sex couples and their families but as a struggle over the very definition of marriage. The couples see marriage as a complex and evolving institution, one that: signifies a permanent commitment between two people; provides stability for their families; acts as a gateway to a plethora of benefits and responsibilities; and acts as a sort of social support and insurance mechanism for when ill health, age and financial setbacks descend on the family. But for the states and their supporting amici, marriage exists primarily as a way of dealing with the unique biological complementarity of men and women, and the need to create an institution to channel the reproductive results of their unions into a normatively powerful institution. And since that’s what marriage means, same-sex couples don’t have the same fundamental right to wed as the Court has repeatedly found opposite-sex couples enjoy.

Pushing off from this essentialist view of marriage, the states’ argument then proceeds roughly as follows: If same-sex couples are permitted to marry, then the institution will be unmoored from its biological anchor, and, over time lose its properly privileged status. At least, they say, we should take advantage of the go-slow approach that our federalist system affords, and let the states continue to work this out, one-by-one, as they have been doing. Marriage rates are already cratering (this much is undisputed) and same-sex marriage will “undermine important social norms…that arise from the man-woman understanding.” They imagine a sort of social Armageddon, with marriage rates pushing further down, unmarried parenting increasing, and—in what the principal author of the “100 Scholars” brief has risibly called “a short and simple causal chain”— an additional 900,000 abortions occurring over the next thirty years. (That calculation relies on the fact that unmarried women abort at a higher rate than married women.)

Well, this might happen. But there are so many moving parts at the macro-social level that predicting anything so specific is foolish. While we’re speculating, why isn’t it just as likely that the example of same-sex couples fighting so hard to marry will reinforce the importance of marriage, serving as an example of the power of commitment to a largely heterosexual population that’s been moving away from it? And no matter what happens, the truth is that we’ll never know whether increases or decreases in marriage rates following a nation-wide ruling for same-sex marriage were “caused” by gay and lesbian unions. (As might be expected, the early data aren’t especially helpful. In states that have already adopted same-sex marriage laws, marriage rates have fluctuated up and down, and each side has, predictably, drawn its own conclusions from the numbers.)

Why are the states and their amici more concerned about the future than the present? Probably, again, because of the need to persuade Justice Kennedy. And they do have at least a slender reed to cling to in their effort to win his likely decisive vote. In early 2013, his mangled metaphor during the Prop 8 oral argument suggested a concern about moving too fast: “The problem…is that you’re really asking…us to go into uncharted waters, and you can play with that metaphor, there’s a wonderful destination, it is a cliff. Whatever that was.”

Perhaps the states can lash this cliff-jumping worry to Kennedy’s federalism fetish, and convince him that the incremental approach is best.

But I doubt it. His more optimistic interpretation of his own metaphor was the right one: equality is “a wonderful destination.” Courts need to address the problem of real people with real grievances rather than worrying about unprovable and improbable consequences. It’s time for the Court to take the final step down the path paved by Justice Kennedy himself.