First, teachers should teach subject matter not proselytize.
That said, I don't know how one talks about Salem without mentioning religion. It's pretty difficult to discuss slave narratives without providing background information on Old Testament symbolism. One should at least mention that Thomas Jefferson spent a number of nights in the White House using a razor to excise the miraculous elements of the New Testament. When teaching the 1890s, explaining William Jennings Bryan's "Cross of Gold" speech is tough if one doesn't explain the allusion. So is discussing Theodore Roosevelt without mentioning his "We Stand at Armageddon and We Battle for the Lord" speech. One should probably mention Sitting Bull's importance as a spiritual leader before mentioning Battle of The Little Big Horn. The last history book I looked at was woefully inadequate on both The Sun Dance and The Ghost Dance.
Further, it's impossible to teach world literature without covering the Bible, Lao Tzu, Confucius, Plato, Socrates, Gandhi, Tolstoy, Dante, or a bunch of wonderful pagan stories. In American literature, those who fear Flannery O'Connor's Catholicism should know that Mark Twain provides a cynical balance. Lest I forget, The Life of Pi should make all moral therapeutic deists happy.
My fellow believers need to own that Christianity has been used as a tool to enslave and kill countless people. Atheists need to acknowledge that Pol Pot, Stalin, and Mao headed murderous regimes that were officially atheistic. Evil people will use any tool at hand to accomplish their ends. On a more benign note, Christians need to acknowledge that the Bible is not a science book while secularists ought to acknowledge that science is an inadequate tool for explaining why the universe should go through trouble of existing.
To move this from the classroom to the full public square, all should try to avoid being deliberately offensive. Everyone needs to realize, however, that there is no God given/Constitutional/civil/human right to go through life without being offended by an idea that differs from one's own. That offense is necessary to build one's mind or soul or both.
The public square needs to look at this clip from an old science fiction series Babylon 5. (The important part starts 15 seconds in. It's American television so there may be a cringeworthy stereotype used to make a broader point.)