Freedom of Religion is not Freedom FROM Religion. The 1st Ammendment protects the public display of that Bible. To prohibit the public display is government CENSORSHIP.
There is no requirement to display the texts of all religions in that display. There is no suppression of other religions.
Atheism IS a religion (it is the belief/faith that there is NO God). Agnosticism says "don't know". Atheism says, "I 'know' there is no God." None of us will know with provable certainty until we die (unless we encounter the divine made flesh).