After the "savages" steal Piggy's glasses in order to make fire, Piggy is virtually blind. He literally can barely see his own hand in front of his face. Clearly he needs to get the glasses back in order to function on the island. He can't appeal immediately to Jack, so he appeals to Ralph, outlining what he'll say to Jack when he does see him.
His argument is a simple one: "I don't ask for my glasses back, not as a favor, I don't ask for you to be a sport..., not because you're strong, because what's right's right."
It's a sensible argument spoken by the character most representative of intelligence and wisdom; unfortunately, Piggy is appealing to the least likely person to listen to reason on the island--Jack. You know Jack's response, I'm sure, and thus the last real voice of wisdom and logic is silenced.