Unfortunately, most people are emotional creatures first. Sometimes only. So facts don’t really matter because they’re engaging on the emotional level of “christian stuff feels good and safe, but other stuff feels dangerous and foreign”. We all do this to some extent. There’s no solution.
People mostly change their mind because stuff coming from their in-group, or horrible trauma.
There IS a solution to this particular problem, namely don’t use schools as a vector for spreading religion.
That’s true for this specific thing, but won’t solve the underlying problem of “things I’m comfortable with are good, and abstract things like facts and fairness don’t matter”