I think this issue boils down to this. Do people have the right to be rude? It is not, “should people be rude?”. We have the right to be rude, but we should be polite to others.
If one is rude, there are likely consequences. That's just a fact of life.
Is it reasonable for schools to determine what behavior is acceptable in the classroom? On campus? I think it is.
The boy in the story passed out invitations in the classroom; had he mailed the invitations, it would be none of the school's business.