From today's Shurtleff v. City of Boston:
When the government encourages diverse expression—say, by creating a forum for debate—the First Amendment prevents it from discriminating against speakers based on their viewpoint [including based on its conveying a religious message]. See Rosenberger v. Rector (1995).
But when the government speaks for itself, the First Amendment does not demand airtime for all views. After all, the government must be able to "promote a program" or "espouse a policy" in order to function. Walker v. Texas Div., Sons of Confederate Veterans, Inc. (2015). {Boston could not easily congratulate the Red Sox on a victory were the city powerless to decline to simultaneously transmit the views of disappointed Yankees fans. The Constitution therefore relies first and foremost on the ballot box, not on rules against viewpoint discrimination, to check the government when it speaks.} The line between a forum for private expression and the government's own speech is important, but not always clear.
This case concerns a flagpole outside Boston City Hall. For years, Boston has allowed private groups to request use of the flagpole to raise flags of their choosing. As part of this program, Boston approved hundreds of requests to raise dozens of different flags. The city did not deny a single request to raise a flag until, in 2017, Harold Shurtleff, the director of a group called Camp Constitution, asked to fly a Christian flag. Boston refused. At that time, Boston admits, it had no written policy limiting use of the flagpole based on the content of a flag.
The parties dispute whether, on these facts, Boston reserved the pole to fly flags that communicate governmental messages, or instead opened the flagpole for citizens to express their own views. If the former, Boston is free to choose the flags it flies without the constraints of the First Amendment's Free Speech Clause. If the latter, the Free Speech Clause prevents Boston from refusing a flag based on its viewpoint.
We conclude that, on balance, Boston did not make the raising and flying of private groups' flags a form of government speech. That means, in turn, that Boston's refusal to let Shurtleff and Camp Constitution raise their flag based on its religious viewpoint "abridg[ed]" their "freedom of speech." …
The majority opinion, written by Justice Breyer and joined by Chief Justice Roberts and Justices Sotomayor, Kagan, Kavanaugh, and Barrett, applied the three-factor analysis that the Court had used in Pleasant Grove City v. Summum (2009) and Walker:
