The Supreme Court will rule for nationwide marriage equality by a 6-3 vote. That's my prediction. This is premature, more than a week before the Justices hear arguments, but here are my reasons -- good, bad, and ugly. If it does happen, this will be why.
Good Reasons
These are more or less squarely legal reasons, the kind you could tell a judge in court without feeling stupid. If the Supreme Court does rule for marriage equality, these reasons will appear in the opinion.
1. What the Law Says
The legal case for marriage equality has been getting steadily stronger. Since 1996, the Supreme Court has twice struck down anti-gay discrimination. In these cases, the Court has said that moral disapproval of homosexuality is not a legitimate purpose for law, and it has looked closely at anti-gay laws to sniff out this illegitimate "animus."
Thanks to earlier decisions, in the Supreme Court and elsewhere, the list of goals that anti-gay laws could plausibly be pursuing, other than just being anti-gay (which, again, is unconstitutional animus) is getting very short. In fact, it may be down to "straight people need marriage to keep them from dropping random babies everywhere." Yes, that is the real argument. No, really. That may be an okay reason for marriage to exist, but it is an excruciatingly lame reason to keep gay people from marrying.
2. What the Law Means
Marriage equality is most likely to be decided under the Equal Protection Clause, which requires the government to treat people alike unless there's a good reason to treat them differently. Notice that this principle, I've just stated it, says nothing about what equality means in practice. To know that, we have to know which differences among people are important, and what kinds of reasons are good. In other words, the Equal Protection Clause works only because the judges who use it have visions of what equal citizenship means -- of which qualities it protects in people and what it allows government to do to them.
In recent decades, he Court has been using Equal Protection to support a sort of identity libertarianism -- a right to be who you are, and not be punished or burdened for that, just as long as you're not hurting anyone else. This has been true in the earlier sexual-orientation cases, but also in cases involving gender (in the male-female sense) and race.
A decision for marriage equality would consummate (for now) a trend toward saying that living under the US Constitution means having the right to be yourself, to live your own life on your own terms, even if those terms are untraditional, unconventional, or disapproved of by most of your neighbors. It would deepen constitutional recognition of the dignity of individuals. It would say that the Constitution recognizes the preciousness and urgency of being one's own self.
Bad Reasons
These reasons are not strictly legal. It's awkward or worse to raise them in court, although most observers agree that these kinds of considerations matter. If the Supreme Court rules for marriage equality, these probably won't appear in the opinion, but observers will be buzzing about them.
1. Personalities
Justice Anthony Kennedy, who will most likely be the decisive vote in the marriage case, wrote both of the earlier sexual-orientation opinions. He is willing to use the Court's power to expand gay rights. His earlier sexual-orientation opinions are full of the moral vision of individual dignity -- so much so that Justice Antonin Scalia, dissenting in one, derided his colleagues "sweet-mystery-of-life" prose as an embarrassment to the Court.
Kennedy sees the Court as playing an important role in updating core constitutional principles, such as freedom and equality. He likes to be on the right side of history, just a half-step ahead of the parade. With public opinion racing toward marriage equality, he this is a golden opportunity to do. Assuming the Court's four liberals would go along, that's 5-4 for marriage equality.
Chief Justice John Roberts doesn't want to be on the wrong side of history. If Kennedy writes a poetic opinion about personal dignity, which most of the country celebrates within a decade or two (and much of it celebrates immediately) that is what dissenting would mean. That's how I get 6-3.
2. Backlash
Although not everyone thinks they should, almost everyone agrees that the Justices think about how the public responds to their decisions. There is some wariness of deciding visible and divisive cases like Brown v. Board of Education, which inspired more than a decade of massive Southern resistance to integration, and Roe v. Wade, which Justice Ruth Bader Ginsburg has suggested may have hurt abortion rights by provoking abortion opponents. Brown is canonical now, and Roe is canonical for many liberals, but the Court has taken a beating for both. It is usually hard to find 5 justices looking for a beating.
It's easy to think, though, that backlash would be mild. In states where a majority still opposes same-sex marriage, many newly married couples live in communities that support marriage equality. The disruption to conservatives' lives would actually be quite mild -- nothing remotely like desegregation, which uprooted a way of life. Although plenty of opponents see same-sex marriage as immoral, unlike abortion no one thinks it is murder. There would be some shouting and stamping against the opinion, but just about the only lives that would change much would be those of newly married couples.
3. Consistency
The state-by-state dispute over marriage has cramped recruitment for companies, universities, and other employers in anti-equality states. Although this issue gets less attention than the others, and has less moral weight, it appeals to an elite impulse in some justices to tidy things up and let labor markets work. The Justices are, by and large, the kinds of people whose friends are employers and mobile professionals. For both groups the country's patchwork of marriage laws is an irrational and irritating holdup.
Ugly Reasons
These are reasons that take a certain amount of cynicism to embrace. You definitely couldn't say them in court, and it is unlikely that most Justices even consider explicitly. They are in the air, though. One way to think of them is as the flip side of some of the other reasons.
1. Marriage Equality Buys Affirmative Action and/or the Voting Rights Act
Justices don't trade votes, among themselves or, in their own heads, from case to case. But the fact that they think about public reception means there is some tug against a series of decisions that feels too political, too partisan. Conservative rulings on affirmative action and federal supervision of state election law under the Voting Rights Act would both be easier to stomach in a year with a big liberal victory. It isn't that anyone would say this, or even think it in as many words. It's just that the whole package would feel easier to do.
2. It Costs the Right Nothing
Again, Justices don't think this way, but their gut feeling about what makes sense does involve their political attitudes. (Remember how liberals and conservatives split 5-4 on the decision that put George W. Bush in the White House.) Opposing marriage equality is increasingly an albatross for the national Republican Party. Considering its base, it will need a while to lose the big bird on its own. A decision for marriage equality would nullify the national issue.
All of the Above
My prediction is a little out there. Despite the political rush toward supporting marriage equality, the smart position among legal experts is still to expect some kind of split decision. The most common thought seems to be that the Court will uphold marriage equality in California without requiring it elsewhere, or will require it only in states that already protect sexual orientation in other ways, while maybe (in a separate case) striking down part of the Defense of Marriage Act. There's really no way of saying who is right. The reasons I've given are why it might go my way.
This would be an amazing thing for progressives, a powerful affirmation of social and cultural progress. Personally, I would be moved to begin seeing same-sex unions in my state, North Carolina, which added the latest of the country's opposites-only marriage amendments to its constitution just last year.
It's a mild irony that the sudden likelihood of a marriage-equality decision highlights just how not-radical the decision would be. The current Supreme Court is very conservative, but its members mostly belong to the coastal culture that has embraced marriage equality across the political spectrum. In this Court's hands, marriage equality would be part of a general libertarian trend, a way of reading the Constitution that also supports ending affirmative action and treating campaign contributions as First Amendment speech. It would be still be a great thing, but part of a larger mixed trend for progressives.
If marriage equality happens this spring, I'd suggest that progressives celebrate the Supreme Court, but not too much. The real credit goes to the brave people who, for decades, have refused to accept that their lives are less than fully human, or that there is such a thing as second-class love. If the Justices find those principles in constitutional language, it will be because ordinary Americans have put them there.