A scapegoat is a person who is unjustly held responsible for a deteriorating situation, or for problems created when things go wrong, often to make a more powerful and controlling person appear blameless. In Lord of the Flies, Jack relentlessly targets Piggy and ridicules him at every opportunity because Piggy's logic exposes much of Jack's silly and risky behavior. In chapter 2, we already see Piggy as an independent thinker with a distinct role, as he calls the other boys "a crowd of kids" and follows Jack "with the martyred expression of a parent," whereas the other boys blindly follow Jack. This foreshadows Jack's response to power and descent into savagery and sets Piggy up as the scapegoat, ultimately contributing to Piggy's own violent death.
Ralph has been voted chief and so Jack is threatened by Ralph. Despite his attempts, he is unable to persuade the boys that his position as "chapter chorister and head boy," as he says in chapter 1, means that he should be chief. Any attempts to minimize Ralph's influence fail because Ralph commands the respect of the other boys. Jack can, however, target Ralph's closest ally, and it does not take Jack long to recognize Piggy's vulnerabilities. A scapegoat always has vulnerabilities, and the unscrupulous and cunning Jack intends to exploit Piggy's to his own advantage.
Piggy is different from the other boys in appearance and thinking. He is asthmatic, chubby, wears glasses, and understands that maturity and adult thinking have a place on the island. Therefore, it is relatively easy for Jack to belittle him when he (Piggy) is the closest thing to an adult on an island without adults. Jack does have leadership skills (but of a very different style from Ralph) and so the other boys are quick to follow his lead in showing a complete lack of respect for Piggy because they do not realize that in so doing they are reducing Ralph's effectiveness.
In creating his main characters, or those with the most influence, Golding has emphasized a character-type for each of them. Simon represents godliness and kindness. Roger represents cruelty and evil. Ralph represents order and patriotism. Jack is power-hungry and Piggy represents logic and reason. Through these characters, Golding exposes man's flawed human nature, and this novel serves as a warning of the fragility of power structures, even democracy. Making Piggy a scapegoat removes accountability from the boys themselves, setting a dangerous precedent for the world as a whole.
In the novel Lord of the Flies, Piggy is an overweight, asthmatic boy who reasons things out and supports an adult approach to the problems of the island. He is the one who suggests how to use the conch which helps keep order and democratic rule in the meetings. Ralph uses Piggy's glasses to start the signal fire which is their one hope of rescue. Piggy is the one to suggest moving the signal fire to the beach where it will be more visible. Because Piggy is now on an island where physical prowess is rated higher than his intellectual reasoning, he is often laughed at or made fun of in some way. Piggy represents the civilized world where rules are followed and sanity prevails. Jack, representing the lawlessness happening on the island, eventually breaks one of Piggy's lenses and steals the other, leaving Piggy blind and helpless in this deteriorating world. Jack gives Roger permission to break the rules from the old world of home, and Roger pushes a huge rock down on Piggy, killing him and destroying the conch of law and order. Now the voice of reason and civilized behavior is gone.