Jack's thirst for power makes him do otherwise unacceptable things
He truly believes that he's entitled to be the leader of the group. His arrogance is so profound he loses interest in the idea of being rescued, only focusing on hunting and the power of taking a life. He misuses the power he takes by abusing the boys and controlling them. The trail of horror directly caused by him is long and extensive.
Jack's leadership lacked complete thought, creating savages out of once civilized boys. He used the thrill of hunting to gain control of the group, as he believed the game of hunting was enough for a tribe to live off of. After going rouge and brainwashing the others into turning on Ralph, his obsession with hunting grew larger. He started to behave in a way that is completely barbaric and chaotic, which would be considered heinous in a civilized society. He loses his grip on reality and became so obsessed with killing it becomes ingrained as the foundation of his leadership. After he takes on the title of "chief", Jack's dominance over the boys grows stronger. After the group successfully killed a pig he said, ''You should have seen the blood!'' Jack was so excited over the killing of a pig he even rubs the blood of the pig onto his hands. He used the boys to fuel his obsession with killing the pigs on the island, as he said, ''Kill the pig, cut her throat, spill the blood.'' This becomes the chant every time a pig is killed. His aggressive behavior led to nothing but disarrayed events, with the death of Piggy and Simon, and the group eventually turning on Ralph wanting to hunt and kill him. During the night of Simon's death, Jack had gone completely unhinged, sitting at the pig roast with his face painted to resemble a hunting mask. Towards the end of the novel, he showed no remorse for the deaths of Piggy and Simon, and for attempting to kill Ralph. " . . . like an idol" while "power . . . chattered in his ear like an ape." His tribe addressed him as "Chief," indicating his way of hunting, barbaric rituals, and sadism had finally won over the boys into becoming ruthless savages.
Jack's power did lead to unfortunate events, but ironically by the end of the novel Jack's authority led to the island setting on fire, which catches the attention of the ship that came to rescue them. If Jack wasn't so relentless, it would have taken longer for them to be rescued. Also, showing the group how to survive by hunting pigs was not barbaric in any way, because they needed to know how to hunt some way or another.
His lust for violence fueled his source of power and savage behavior.
Rejecting the premises
His source of power was fueled by the need to survive, not in violence.