So Many Stupid Kings
Our favorite scumbag marches his posse into Lamanite territory and somehow convinces their king that they need to go to war against the Nephites. The king makes a weird, panicky decree across his entire kingdom that everybody has to go to war, and many people are too scared of the Nephites to obey. So, following the Book of Mormon's proud tradition of stupid, gullible kings, the Lamanite ruler then gives Amalickiah command of the part of the army that actually answered the call.
Let's say an unknown out-of-towner wanders into your kingdom with the message that you really, really need to declare war on your neighboring country. And let's say this makes you so nervous that you basically try to draft every able-bodied man in your entire nation into the military. A lot of people take issue with the very real possibility of being forced to die for their country, so not everyone who's drafted actually shows up. What's the best course of action? Do you use your existing leader of the army to force everyone to comply? Or do you give control of the army to the guy you just met who's heavily influenced your last two major decisions and let his inscrutable and unpredictable motives wield the full power of your national military might?
Idiot. No wonder he gets murdered for his throne.
Socially Progressive Lamanites
Amalickiah takes the army and goes to confront the group of draft-dodgers who, strangely, have gathered in a defensive position so that they can fight for their right not to have to fight. Amalickiah manages to convince their leader, Lehonti, to bring his armies down from their mountain stronghold and surround his recently-acquired Lamanite army under cover of darkness. Rather than die, the Lamanite army agrees to unite itself with the dissenters under Lehonti's leadership. Amalickiah then has an associate poison Lehonti so that he can ascend from second-in-command to supreme leader. When he marches the whole group back to the king, he has one of his cronies stab the king to death and blames it on the royal servants. After chasing the king's servants out of the country and using their flight as evidence of their guilt, he has effectively gained the support of the people. Then he marries the queen and completes his rise to total power over the Lamanite nation.
This could never have happened if he'd been a Lamanite trying to usurp the Nephite throne.
This plan of Amalickiah's only worked because the Lamanite king trusted him despite his white and delightsome skin, because Lehonti trusted him (albeit hesitantly) despite his white and delightsome skin, because the Lamanite queen trusted (and married) him despite his white and delightsome skin, and the rest of the country supported him as the king's replacement despite his white and delightsome skin. While this kind of open-mindedness clearly allowed the Lamanites to be manipulated, it also means they're better people than their God-favored neighbors. They don't exclude people from their society based on skin color or perceived moral inferiority, and that makes them even more enlightened than the god their white and delightsome peers tend to worship.
Apostates Are More Evil Than Non-Believers
The chapter closes by discussing those among the Lamanites who were, like their new king, former Nephites:
Now these dissenters, having the same instruction and the same information of the Nephites, yea, having been instructed in the same knowledge of the Lord, nevertheless, it is strange to relate, not long after their dissensions they became more hardened and impenitent, and more wild, wicked and ferocious than the Lamanites—drinking in with the traditions of the Lamanites; giving way to indolence, and all manner of lasciviousness; yea, entirely forgetting the Lord of their God.This is a common misconception held by faithful Mormons, which is helpfully given a scriptural basis. This verse is basically saying that once a Nephite leaves his pious society, he forgets how not to be a completely awful human being. Not only will he abandon his religion, but he'll also become evil, savage, violent, lazy, and sexually deviant.
People need to be more cognizant of the fact that religion can neither claim a monopoly on moral behavior nor guarantee that its devotees will exhibit such behavior. There are plenty of wonderful people who are atheists (or ex-Mormons) and plenty of atrocious people who are loyally seated in LDS chapels every Sunday morning. Anyone who's ever spent time with someone from a religious background different from his own should know this. And anyone who reads this verse should immediately disregard it as severely oversimplifying the spectrum of human conduct.