People have very different ideas about what constitutes "decent discourse", and the law shouldn't distinguish between those. Hence Fred Phelps and his sorry excuse for a church continue to run around the country delivering what they believe is an urgently important religious message. What should a school do if a student with that sort of religious beliefs earns a valedictorian spot? Even with specific recognized obscene words barred, and replaced with respectable synonyms, most people would much rather be subjected to the "How I lost my virginity speech. And what about white supremacists, who certainly have a right to express their political views, and who often practice their beliefs within the context of an organized religious group?
I'm not suggesting that schools should be allowed to apply a different standard to religious speech by valedictorians, than to any other type of speech. But I think it's also acceptable for a public school to apply a standard across the board, limiting valedictorian speeches to material which wouldn't offend any significant number of reasonable people in the community. And while I don't think it's reasonable for anyone to be offended by a student describing his/her own religious faith and the role s/he believes it played in his/her academic success, I do think it's reasonable for anyone who doesn't share the student's specific religious beliefs to be offended by a speech which amounts to aggressive proselytizing. This is why I think we need to know what this student was startig/planning to say, before passing judgement. An auditorium holding many Catholic, Jewish, atheist, agnostic, and other non-evangelical Christian parents who are their to witness their own children's graduation, shouldn't be given a choice between listening to speech which the speaker and the school officials both know will offend them, and getting up and leaving their own child's graduation. Neither should an auditorium full of religious parents be forced to sit through a militant atheist diatribe, in which the speaker admonished them and graduating classmates that they can't aspire to high academic achievement unless they give up their stupid superstitions.
The refusal of courts to allow public schools to set reasonable limits on students' speech, behavior, and dress, has been a huge contributor to descent of public schools into an anti-civilizing force. It's only in very recent years that courts have begun to uphold dress codes. For a long time, if a girl wanted to go to school in a teensy midriff-baring halter top and teensy low-rise "hot pants", the school wasn't allowed to interfere with her right to "free expression". Finally, courts started coming around to the idea that reasonable limits on student attire were appropriate and permissible, and they should come around to that idea about ALL kinds of speech as well.
Welcome to America of the 21st Century where Christian speech is offensive and Christian subject matter deserves a PG-13 rating.
Last I checked there is a right to freedom of speech. There isn't a right to not be offended. Free speech wins.
Finally, courts started coming around to the idea that reasonable limits on student attire were appropriate and permissible, and they should come around to that idea about ALL kinds of speech as well.
The truth of the matter is that before politically directed interference by the ACLU against public schools, those schools could always limit what they considered vulgar or inappropriate clothing, language, expression, and even attitudes that were over the top.
The leftist crowd led by extremist groups like the ACLU began to use parents and students to sue schools and school boards that did not give up on 200 years of American culture and begin to let any vulgar dressed, foul-mouthed, students spread the ACLU's anti-God political revolution to reinvent America through the government monopoly of education.
The ACLU types needed to use people for progressive lawsuits so that the leftist courts could get involved and 'walla', the leftwing revision of the public schools and the law was in place.
Students who served the left's politics, subversive intents, and anti-God revolution we not limited by the ACLU in any way. They never come out against speech that advances their leftist cause, they only sue those who stand with 200 years of American culture and morality which the ACLU fights with all its energy.
The ACLU types only began to step in if a conservative religious person spoke up with a forcefullness approaching that of the decades of anti-Christian vulgarity and leftwing politics that fights against the ACLU humanist utopia.