You're absolutely right, and the judge was absolutely right. If you let the hymn in, then some islamist would demand that a muslim chant be put in also. And no way would I want a kid of mine exposed to a muslim chant.
The only way took fix this would be by a constitutional amendment declaring this to be a Judeo-Christian country. And that ain't gonna happen.
They are getting their chants in regardless.
How about letting each High School exercise their God Given freedom to perform as they see fit? Just as the US Constituition guarantees? Since Moslems don't have music, I don't see much competition.
The only fix is to separate the government from education, so that these football games would not have any sort of government-related implications.
Who cares what some islamist would demand? The proper course of action would be for the district to ignore the demand and ignore any judge who tells them to do otherwise. It's a local matter. Singing a religious song is not establishing a religion. If it comes to that, the Constitution is silent on states or localities having established religions. It's Congress that "shall pass no law" establishing a government religion.
States that insist on banning religious practice or official toleration within their own constitutions are free to do so. Other states are free to do otherwise—countenancing some and not others, or apportioning more "air time" to some religions than others.
Now is the time to have this fight. The Constitution makes sense, and it says what it really says—not what a handful of 20th-century Communists on the Supreme Court decreed in fortune-cookie aphorisms.