"Shall we also never discuss the history of music in music lesson? Or biology in a PE lesson? Lets not look into Freuds ideas on psychology either, far too unscientific"
I guess context is everything. it;s the foregrounding of creationism that is problematic - teaching it as an equal alternative to evolution. There is no alternative explanation of how we came to be.
But that said, religion has played a major part in how we think, organise our societies, power inequalities, demonisation of homosexuals and women and within that context it should be studied.
And science is never conducted in some vacuum where morals and assumptions don't come into play; psychology has played its part in the pathologisation of homosexuality and women and that scientific context should also be studied. Even Freud.