There's no free speech in front of the U.S. Supreme Court — or so says the U.S. Court of Appeals for the D.C. Circuit, which on Friday upheld a 1949 law that says you can't assemble or display signs on the plaza in front of the courthouse.

The decision contradicted a 2002 ruling by the same court that allowed free speech on the grounds of the U.S. Capitol, just across the street from the court. It rested on a combination of architectural analysis and insistence that judges and courts should be more insulated from the public than politicians and legislators.

With all due respect to the D.C. Circuit, architecture is beside the point. What's sometimes called the second highest court in the land was being much too deferential to the highest. The Supreme Court frequently decides high-profile, politicized cases with no single correct legal answer. It stands for free speech. Limiting speech on the plaza is not just a legal mistake. It's a symbolic one.

The court analyzed the law in two steps. First, it asked whether the plaza in front of the court is a traditional public forum or a nonpublic forum. In a different case, the Supreme Court itself had held that the sidewalk in front of the plaza is a public forum. And the district court that ruled in this case had extended this logic to the plaza.

The appeals court on Friday said the plaza wasn't a public forum. It emphasized that the plaza forms an integrated architectural whole with the steps and the courthouse building as designed by Cass Gilbert. The opinion even quoted a statement by Justice Stephen Breyer to the effect that the building's plan "leads visitors along a carefully choreographed, climbing path that ultimately leads to the courtroom itself."

Today, for security reasons, visitors actually can't use the front door to the court, which would lead them from the plaza to the courtroom. But that really doesn't matter. The point is that architectural coherence isn't a good measure of whether a space is public.

A case in point is the grounds of the Capitol, designed by Frederick Law Olmsted, probably the most important landscape architect in U.S. history. They're also designed to be integrated with the Capitol. Yet in the 2002 case Lederman vs. U.S., the D.C. Circuit ruled that the Capitol grounds constituted a public forum and struck down no-demonstration zones there.

The court distinguished the Capitol grounds from the Supreme Court plaza just across First Street by citing a statement made by the Supreme Court this past April in a case called Williams-Yulee vs. Florida Bar to the effect that "judges are not politicians."

Politicians, the court said, must be responsive to the public, and therefore must allow free expression on the grounds of the legislative building. Judges have no such obligation.

The Supreme Court made this point in the course of upholding a Florida rule that prohibited candidates for judicial office from soliciting contributions directly. But limiting the free speech of judges because they aren't politicians is a very different thing from limiting the free speech of the public near the courthouse on the ground that judges needn't be responsive to public opinion.

Protesters outside the Supreme Court aren't primarily trying to influence what goes on inside. They're participating in the national conversation that arises around Supreme Court arguments and decisions. They go to the plaza in part because the television cameras go there. The television cameras go there because the Supreme Court is where the story is.

The reason for that, of course, is that many of the court's most important cases are profoundly political. The justices aren't elected politicians. But they are statesmen and stateswomen. And what they do is very much part of the American political process.

Having held that the plaza is a nonpublic forum, the D.C. Circuit went on to rule that restricting assembly and protest signs there was reasonable because it served the purpose of "maintaining order and decorum at the Supreme Court." Even if you agree with the idea that the plaza isn't a public forum, you might still think this second conclusion was incorrect, and that the court therefore got it wrong.

Inside the courthouse and courtroom, order and decorum are reasonably important. The justices may not need to wear black robes or appear like demigods from behind a red velvet curtain. But mystification aside, they have jobs to do that would be impeded by protesters or signs inside. The court's marshals won't even let members of the public fall asleep during oral argument — if you do, they'll come over and nudge you.

But outside the building, adjacent to the public sidewalk, there's really no need to ban rallies or signs. The main staircase isn't only closed to the public — the justices and employees don't enter there, either.

The true function of the plaza is to create an open public space in front of the people's court where the people can congregate. And like it or not, in a democracy, the people don't always show order or decorum. It isn't reasonable to block the public from speaking or gathering in numbers in a place where it's already allowed to be. The message of restriction is exactly the opposite of what the court should be communicating to the public.

Judge Sri Srinivasan, who wrote the opinion, is as likely as any judge in the country to make it to the Supreme Court one day. He's an excellent judge, and before that was an excellent Supreme Court litigator, arguing 25 cases before the court and serving as deputy solicitor general. His respect for the court is admirable but in this case goes too far. The Supreme Court probably won't overturn the D.C. Circuit's judgment or even take the case. But it should.

Bloomberg View columnist Noah Feldman is a professor of constitutional and international law at Harvard University.