However, I don’t understand how what you are saying singles out Mormonism. I see why it applies to Mormonism. It seems to apply equally to almost any historical text. If the Book of Mormon has value because it’s antiquated ethics cause you to question your own, shouldn’t this apply equally to most any historical text?
If all you had was the Book of Mormon as guidance and not post-modern philosophy as well, I wonder if it ever would have caused you to question your values at all. If causing you to question yourself is what makes the Book of Mormon valuable, shouldn’t authors like Derrida be far more valuable for their having directly proposed this approach? Why bring the Book of Mormon into this at all, other than as one particular example among many? Why give Mormonism credit for something you learned via Derrida?

For a brief while after leaving Mormonism I became a Baha’i. While I no longer am one, I still feel an affinity for many of it’s teachings.
One thing in particular that was able to radically change my perception on religion in general is that we can expect more out of religion.
This faith began around the same time as Mormonism, in a culture far more oppressive, yet from the beginning they taught gender, racial and economic equality as well as independent investigation of the truth.
From this I learned that it isn’t unreasonable to expect Prophets to actually behave like Prophets. To rise above their culture and teach values which many cultures won’t arrive at for more than one hundred years. Rather than lag behind culture, playing catch up only decades later.