why are ralph, piggy, and the twins hesitant to admit being ath the dance

Simon is murdered during the frenzy of the dance. The boys are ashamed of their part in what happened; physically they're exhausted, but they are far more bruised on the inside than the outside

Piggy tries to deem Simon's death accidental, hoping to throw off his cloak of guilt and pretend the fault belonged to no one. Ralph on the other hand, is crazy (literally) with guilt. He holds onto the conch (symbol of power) and claims they've done murder, and they have......... but Piggy denies it. The four are hesitant because they understand what they've done, and they know they've done wrong. This reaction proves that there is still some semblance of knowledge between right and wrong on the island. But the best part of 'right and good' had been murdered.