The short answer to the Foundation’s Winter Solstice request was that the Supreme Court has long permitted exhibits like the Warren holiday display, and the Establishment Clause does not convert these displays into a seasonal public forum, requiring governments to add all comers to the mix and creating a poison pill for even the most secular displays in the process.The court also concluded that the mayor's letter rejecting FFRF's request, despite some questionable statements in it, did not turn the city's holiday display into an impermissible establishment of religion.
Finally, the court emphasized the the holiday display involved is "quintessentially government speech." Quoting the 9th Circuit, it added: "Simply because the government opens its mouth to speak does not give every outside individual or group a First Amendment right to play ventriloquist." The Detroit Free Press reports on the decision.