Our Constitution guarantees the freedom of religion, not freedom from religion. Furthermore, it merely states "Congress shall make no law ..." It does not authorize local officials to either prohibit the free exercise of religion nor to advocate any specific religion. Displaying Bibles is free speech, protected by the Constitution.
Christians have as much right to offer Bibles on public property as do Muslims to offer Korans or Mormons the Book of Mormon. I may not like that, but it is the law of our land, and thank God! The Bible is considered a holy book by many religions besides Christianity, Islam included. So the presence of a Bible is not specific to just one religious viewpoint.
Religion aside, the Bible is the greatest book of antiquity and the human story. It has been demonstrated historically accurate for centuries. It is the best selling book every year in the United States. The majority of human beings on Earth read it and benefit from it.
Various courts have tested this question before and the Supreme Court has reiterated that free speech does indeed extend to public school property as long as school staff are not advocating any one particular religion on school grounds. You're making a mountain out of a molehill.
Robert M. Sexton