In many fanfictions, the scenario of Naruto and Itachi killing the Uchiha clan is a very interesting but also controversial topic. One aspect could be the change in Naruto's character. Usually, Naruto stands for justice and protecting others. If he were involved in such a massacre, it would be a huge deviation from his original character. Maybe in the fanfiction, there could be some extreme situations that force him to do so, like being mind - controlled or having some false information.
In some fanfictions, a possible motivation for Naruto could be to prevent a greater evil. Maybe he was tricked into believing that the Uchiha clan was about to start a war that would destroy the entire ninja world. So, he thought that by taking part in killing the clan, he could save more lives in the long run.
In " Dragon Clan ", Lu Mingfei sacrificed his life to deal with the King of Earth and Mountain. The plot of the story entered a broader world, including more complicated interpersonal relationships, more massive wars, power struggles, and so on. In this world, the conflict between the dragons and the humans became more intense, and Lu Mingfei became a stronger leader, leading the war between the humans and the dragons in a brighter direction. However, even if everything was resolved, it did not mean that the story was over. It represented the beginning of a new story.
Well, there could be various reasons. Maybe there was a deep-seated family conflict that escalated beyond control, or Jeffrey might have been influenced by external factors like drugs or a traumatic event.
It could be that the Moore was mentally unstable or influenced by external factors that led him to commit such a horrifying act. There might have been financial problems, jealousy, or a history of abuse that culminated in this tragic event.