If you wore a shirt that says “there is no god” you would likely be sent home. It’s antagonistic, regardless of how you feel on the issue.
I know if I was a 7th grader and this stupid little shit and his dickhead friends wore this into class, I would feel it was equally antagonistic, except far worse because it seeks to upset a minority that is already going through the wringer.
It runs contrary to the purpose of a school, which is to educate. Your other examples are more of a case-by-case thing, but if a Christian student said they were offended by that shirt, then the student might be asked to not wear it in the future.