Why do Ralph, Piggy and Samneric lie about their part in Simon's death, or use the darkness as an excuse?
Ralph, Piggy and Samneric are the three boys who are most conscious about what is happening on the island. They understand, on some level, that as a community they are degenerating into animals, some into cruel and vicious animals, and are doing what they can to prevent it. They can not admit that they themselves got caught up in the frenzied emotions that caused Simon's death, and as three people who cared for Simon, they can not face their own guilt. Lying about it is the only way they can accept it.