The Nephites were on the defensive here, defending their families “even unto bloodshed.” If Captain Moroni had been on the offense, or if this had been some kind of war for aggrandizement or conquest, it would have been much less honorable to use trickery or deception. There was no ancient equivalent of the Geneva Convention, but there were customary rules of engagement and ways in which wars were fought. However, the Nephites were defending themselves from an attack and their enemies were not playing by the rules.
One of the rules of engagement under Deuteronomy 20:10–12, was that an Israelite attacker had to announce to a city that they were going to attack it. “We are about to attack you, and you have a choice; you can surrender, here are the terms, or we will obliterate you.”
The Zoramites and their new allies were coming in from three directions. They had warriors coming from the north, west, and south. These armies were coming from different lands, and the Nephites were caught in the middle. Even under those conditions, Moroni was apologetic about having to use a stratagem, but I think he was justified. At the same time, as the battle raged and their stratagems were paying off, what really got the Nephites through was their loyalty and commitment to their cause. They were not imperialistic or in search of conquest; they were defending their land, their people, and their sacred things.
Book of Mormon Central, “How Can the Book of Mormon Provide Peace and Meaning to Those in Military Service? (Alma 43:47),” KnoWhy 496 (January 1, 2019).