His entire family had decided to betray the village and this had condemned all the members of the clan, even the children. The killing of the children would have prevented any possible revenge, breaking the trail of hatred. In fact, the trail of hatred is not interrupted because Sasuke remains imprisoned by it. Itachi's love stems precisely from the fact that he decides to sacrifice himself in order to save his little brother and also allow the survival of the clan. In fact, officially the Uchiha clan is not exterminated by order of the authorities but by a thoughtless act on the part of one of its members. So no one is aware of the betrayal.
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