The student's right to express themselves was removed, that sounds like a violation of their first amendment rights. If the school had a policy in place that would have been one thing, but the kids followed the rules set forth and their speech was still limited. 

If the government came in and said that you were no longer able to express your opinion on anything in any public forum but you didn't go to jail, your rights would still have been stripped. If that did happen, you would have my support no matter how wrong your opinions are...