War is brutal, but warfare also has sets of culturally determined rules. In later Mesoamerica, the Aztec Flower Wars were almost ritualized, but were wars-by-appointment, designed for personal glory and for the capture of prisoners to sacrifice to the gods. Such wars have rules, and when the rules are obeyed, everyone understands the limitations.
Mormon’s lament that his commands are not followed comes as an introduction to verse 19, which contains the examples of the types of things that are happening that are not the result of Mormon’s commands. Mormon’s army as become “alike brutal, sparing neither old nor young.” The Nephite army faced a situation where the rules of warfare had been changed unilaterally. The way that they had fought might be seen as a collection of “gentleman’s rules” of warfare. Those “gentleman’s rules” had been horribly violated in this new destructive style of warfare.
No doubt for a while the Nephites maintained their honor in maintaining the old rules in the face of an enemy who was violating them, but clearly the result of constant combat with this new style infected the hearts of the Nephites, and they began to imitate their enemies. Thus did they become “alike brutal”. Mormon now uses the Nephite “women and children” as moral witnesses to their own men’s transformation into the type of army they are fighting. The “women and children” maintain the “proper” understandings, and it is the fighting men who have become brutal and loving of “everything save that which is good.”