Ammon provides information about the decision that the sons of Mosiah made to leave the land of Zarahemla and that Mormon did not give us when describing that event. Mormon told only of their petition to their father (see Mosiah 28:1–3). In this account we learn that their decision was more openly discussed and that there were many who did not believe that it was a wise decision. “They laughed us to scorn.”
The Nephite hatred of the Lamanites was reciprocated by the Lamanites toward the Nephites. The clear enmity suggested that there would be no expectation of success. The Nephite “suggestion” was that, rather than preach to them, the sons of Mosiah should “destroy them.” None of that information was part of the original story as Mormon told it.