In the latest of many cases over the years, the Supreme Court told a Milford, New York, school district that if it opened its doors to some civil and social organizations, it had to open its doors to the Good News Club, a chapter of Child Evangelism Fellowship.

"When Milford denied the Good News Club access to the school's limited public forum on the ground that the club was religious in nature," Justice Clarence Thomas wrote for the 6-3 majority, "it discriminated against the club because of its religious viewpoint in violation of the free-speech clause of the First Amendment."

The principle was the same as that in 1981, when the Supreme Court told the University of Missouri at Kansas City to open its doors to religious organizations. And again in 1993, when a Center Moriches, New York, school district was also told not to exclude religious organizations. And in 1995, when the court told the University of Virginia that if it paid for the printing costs of student publications, it also had to pay for a student-run religious publication. The State may limit speech—it doesn't have to open the door to everyone—but it cannot exclude groups on the basis of their viewpoint, including their religion.

What's especially important in the Good News Club decision is that the Supreme Court lifted this principle so high. It does not matter if the group evangelizes. It doesn't matter if it worships. It doesn't matter if it discusses religious topics rather than secular topics from a religious ...