What is William Golding's message about evil, human nature, savagery and civlilisation or "mankind's essential illness" in Lord of the Flies, and how does he use Piggy to create this message? How does this link to context?
In Lord of the Flies, William Golding presents the idea that, while we may have our good traits, we are all essentially born evil, and it is due to the constraints of civilization that we don't act upon these evil inclinations. Hence, once the boys were removed from civilization by being stranded on an island, they progressed deeper and deeper into their evil natures, with some characters showing more evil characteristics than others.
We can tell Golding is characterizing all the boys on the island as having an evil side because even the characters who are generally benevolent have their darker sides. For example, even the leader Ralph is portrayed as having a dark side in the very first chapter of the book when he mercilessly teases Piggy about his name. Piggy too shows his evil side when he, along with Ralph, becomes swept up in the savage dance with the other boys that leads to the murder of Simon.
While Piggy's unwitting participation in the dance portrays the evil side of his human nature, it's Piggy's love of civilized law that portrays the good aspect of his nature that has been molded by civilization. Piggy's glasses particularly symbolize civilization because, without the glasses, the boys have no way to make fire, which means no cooking, no heat, and no way to signal that they need rescuing. Piggy's love of civilized law is expressed throughout in the way he values the conch and the democracy it stands for but also strongly in his final speeches prior to his murder:
Which is better--to be a pack of painted Indians like you are, or to be sensible like Ralph is? ... Which is better, law and rescue, or hunting and breaking things up? (Ch. 11)