Comments by "Zudabaker" (@Vyrus36) on "WatchMojo.com" channel.

I think the point being missed here is that he was supposed to be unecisarily cruel to show how far he was slipping from his humanity. It even started at the begining of the serries that the longer he stayed there the more he was becoming undead (the role of Ainz) and loosing his human emotions. He also states how he already has no sympathy or kinship for humans going into the world. Meaning that the longer he is in game, the more his sense of humanity slips. He has no problem sending out people who have done far worse to humans than he had before this happened. He had no problem abandoning the adventure group that raided Nazarick in the first place to go and kill them all off. You can tell how far he is slipping by how his right hand man Demiurge keeps blabbing off about what he thinks Ainz is doing and he just goes along with it. Kind of shocked at first, but then laughs it off and becomes totally fine with the role of the supreme being that plans of killing everyone off and taking over the world. It's basically the story of the crazed maniac taking over the world from his perspective going from fair ruler that want's to help to sinister, angry, cruel, conquerer of humans. The "unecessary cruelty" was to show how far Ainz would go to streagnthen his forces when enraged and to show how removed he has become from his human sense of morality. Nothing more, nothing less. And it does have a draw, in the same way people watch documentaries on serial killers. It's interesting because it shows how far his human morality and how out of touch he's becoming with the human world and demonstrates what he is becoming capable of.
1