The choir boys are a unique group in the text because they are unified before their plane crashes on the island. This sense of unity due to their choir robes, their identity as a choir, and their willingness to follow Ralph contribute to their mob mentality. They follow Ralph blindly and willingly because he offers them a reprieve from rules, order, and an adult influence.
As the text progresses, Ralph offers them an outlet for their repressed feelings and allows them to be animalistic. When they feel threatened by a perceived "beastie" on the island, he offers them protection. Ralph is a master manipulator in one sense; he understands that being an outcast is far worse than being part of a group that does unsavory things. Unfortunately, the mob mentality that dictates the choir boys' actions, leads to their ultimate destruction. First Ralph and his hunters kill the sow. She is the only source of food on the island (if they kill the sow, there will be no more piglets to hunt). Then, the boys are entranced by the storm and dancing around the fire while chanting, "Kill the Beast! Cut his throat! Spill his blood!"They become primal and irresponsible. As a result, they kill the only source of good on the island: Simon. Lastly, in an attempt to "smoke out" Jack, they begin a fire that destroys the island, but ultimately rescues them.
As a group, the boys could be described as primal, but they are not entirely evil. Although Roger embodies evil, and he wants to harm others without consequence or concern, the other choir boys are acting as a unit rather than individuals. An example of this contrast is when Roger is lurking in the brush just along the beach. He is purposely throwing stones at the little'uns playing in the tide pools. Golding suggests that Roger purposely misses (implying he could easily hit the boys with rocks) because "there was a space round Henry, perhaps six yards in diameter, into which [Roger] dare not throw. Here, invisible yet strong, was the taboo of the old life." By the end of the text, Roger is not restrained by societal constraints and does not miss when he launches a boulder at Piggy killing him. When you observe the remaining choir boys/hunters at the end of the text, they begin to cry when they are rescued because they realize the destruction they have caused.
The choir boys are chosen to be the hunters by Ralph after he wins the vote to be a chief of sorts for the boys on the island. Jack is not happy about losing the vote and in order to appease Jack, Ralph makes Jack the leader of the choir boys and hunting party. Jack, being the leader of the hunters, is representative of the group as a whole. Jack, and the group, are basically blood thirsty killers. They are selfish, and do not have the good of the group in mind. That can be evidenced by their desire to hunt and kill pigs more than making sure the fire stays lit in order to signal a rescue.
As for a quote that highlights the bloodthirsty nature of the choir boys, my favorite is the quote that describes Roger as he pushes the boulder off of the mountain that kills Piggy.
"High overhead, Roger, with a sense of delirious abandonment, leaned all his weight on the lever."
"A sense of delirious abandonment" is sadistic. It's a phrase that I would describe a psychopath with. He is finding a ridiculous amount of pleasure from causing pain on other people. That's dark.