Piggy is an interesting character--one that is open to multiple interpretations. Piggy displays characteristics that should make him an important leader among the boys; however, Piggy is almost universally mocked and even despised by the others. Golding shows that prejudice and rejection of the "other" in a society can deprive it of the full contributions of its highly talented members--to the detriment of the rejected individuals and the society. Piggy is intelligent, has creative ideas, and has a natural bent toward administration. These are attributes that should have been valued by the boys and would have enriched their life on the island if fully utilized. However, Piggy is perceived as "other," causing the boys to discount many of his words and ideas:
"Piggy was a bore; his fat, his ass-mar and his matter-of-fact ideas were dull. ... There had grown up tacitly among the biguns the opinion that Piggy was an outsider, not only by accent, which did not matter, but by fat, and ass-mar, and specs, and a certain disinclination for manual labor."
Golding gives this description from the point of view of the boys; it must be taken with some irony. Although his "accent" is downplayed in this passage, it is a big part of what makes Piggy "other." He comes from a part of England that is not respected by the boys who come from a "better" part of the country. His appearance (fat and specs) also makes him unlikable, which reveals the shallowness of the boys' standards for friendship. Although Piggy doesn't have physical strength and stamina, they are made up for by superior talents in other areas. And although Piggy's personality is unpleasant, that can probably be attributed to the way others have always treated him.
When evaluating what Golding was trying to do with Piggy, one must consider not just his intelligence, but also the other qualities that Golding worked into the character. The way the boys treat Piggy, ignoring him to their own detriment, reveals the propensity people have toward prejudice and the negative consequences of prejudicial attitudes on society.