The court will consider two cases: California's Proposition 8, which singled out gay people and denied them marriage in that state; and the federal Defense of Marriage Act, which singles out legally married couples who are gay, and denies them federal benefits.
The stakes are particularly high in cases like these. We're talking about singling out a group of adult couples and denying them a benefit based on a religious book which judges their mutual love to be inferior.
Now it's true, that's the way the law stands in most states right now - and it's tempting to embrace what appears to be a majority view but as generations pass and public opinion evolves, what seems the "practical thing" could end up looking very different.
And I thought columnist EJ Dionne made a good point on Meet The Press, "I have a friend who has worked for a fairly conservative Christian institution for a long time who said, our problem isn't that gay and lesbians want to get married, it's that they're the only people who want to get married."
An exaggeration, of course, but the Supreme Court finds itself being asked to discourage monogamy among the very couples who seem to be the most eager to embrace it, on the grounds that their form of monogamy is objectively inferior.
Plenty of people have drawn a parallel to 1857 - when the Supreme Court tried to settle the slavery issue by ruling decisively, 7-2, that under the Constitution, due to their inferiority, African Americans did not have the rights of citizens. Seemed like the practical thing at the time. And yet I think we all agree that's one they probably wished they could do over.