I agree that the bible is not "banned" in American public schools. As I wrote earlier, it is unconstitutional to legislate the bible as religious in the first place. I disagree with your assumption that grown adults may not distribute religious texts to a captive audience. Where schools get their authority to ban certain books, be they religious texts or comic books is from the Tinker vs Des Moines decision which ruled that the school "must be able to show that [their] action was caused by something more than a mere desire to avoid the discomfort and unpleasantness that always accompany an unpopular viewpoint". What we have here is not the school banning anything, so there's no problem and certainly no violations of constitutional rights of students.