The Supreme Court will hear arguments today that could lead to a constitutional right for gays to marry.  Many court watchers believe it's a done deal already.  In addition to the four liberal judges, Justice Anthony Kennedy has already ruled with the majority three times against maintaining a ban on same-sex marriage.  He would appear to be the fifth vote that would make gay marriage the law of the land.

But nothing is certain, which is why some observers believe that Chief Justice John Roberts may be a pivotal vote on the question.

New York Times:

Putting aside previous cases and previous votes, there are a number of institutional reasons Chief Justice Roberts might, and should, cast a vote for the freedom to marry.

First, a Supreme Court ruling authorizing the states to restrict marriage to heterosexual couples would lead to enormous confusion. The court’s decision not to take appeals of earlier cases, or put other appeals of lower court decisions on hold, has induced many couples to marry. Surely, same-sex couples who married when marriage was legal under prior court rulings would remain so. But if the plaintiffs do not prevail, all of the states that recognize the right of same-sex couples to marry in light of lower federal court rulings could revert to their earlier state of affairs.

(A ruling against the plaintiffs would leave untouched the rights of same-sex couples to marry in the states that have affirmed the right through legislation, ballot initiative or state constitutional rulings.)

The consequences of such a ruling would be dramatic — and quite unsettling. Administrative agencies would have to shift policies (again), create new forms (again), and educate their bureaucracies on a variety of matters — all of which could be undone by a new legislative act or state constitutional amendment. Given the sheer number of economic rights, presumptions and obligations that travel under the “marriage” heading, denying gay couples access to a uniform institution, with all the complications, headaches and (possibly) litigation it could bring, seems like the antithesis of restraint.

Then there is the broader issue of social consensus. The continuing nationwide division over same-sex marriage, notwithstanding the recent shift in public opinion, might give Chief Justice Roberts pause. He may find it unwise to put the Supreme Court’s blessing on a legal rule that would create so much uncertainty for so many people in such a bedrock institution.

Being chief justice, Roberts would also have the opportunity to write the historic majority opinion if he voted for gay marriage.  Supreme Court justices are not immune to vanity, and if Roberts did author the opinion out of some kind of elevated sense of his own worth and a desire to make history, he wouldn't be the first.

But a far more compelling reason for Roberts is, as the article points out, the mass confusion that would ensue if gay marriage in many states was shot down.  The Supreme Court is in love with precedent and hates to create the kind of confusion described above. The history of the court, from civil rights through abortion and other cultural issues suggests that legal momentum for change has reached the critical stage and backing off now would cause more trouble than the decision is worth.

Not a very elevating reason for allowing gay marriage, but that's the reality faced by same-sex marriage opponents.