I suspect that a lot of Christians don't read the Bible as a cognitive defense mechanism since a cursory reading shows that there's a lot of material (especially in the Old Testament) that is at odds with modern morality.

The history is more complex. For many centuries, lay Christians weren't supposed to read the Bible, and in at least one time and place, translating the Bible into English was deemed heretical. That changed with the Reformation, one of the pillars of which was the view that the Bible should be read by all, as the sole basis of religion. And it was (or listened to, by the unlettered).

If (cite?) those who call themselves Christians do not nowadays read the Bible, it is not clear why the alleged cognitive hazard did not apply, say, in Victorian times. Perhaps they are merely more lacklustre about their religion.