The existence of the Bible is historical fact and artifact. There is historical merit in studying the various religious beliefs of historical peoples that factored into their values and thinking. Protestantism is factually a thing. Different colonies and denominational belief is a thing and a topic in American history. What made Quakers Quakers and how did that impact the Pennsylvania.

There’s a difference between teaching the bible, teaching theology, and teaching histories of religion. There’s definitely questions of what we are teaching and what is appropriate in public primary and secondary schools and in what subject, but I don’t think there is anything in and of itself bad if the historical religious beliefs and impact on historical civic life are discussed.