Why does Piggy believe that Ralph must regain control?

In Chapter 5, Ralph leads an assembly where he discusses the true identity of the beast. Jack believes that a beast does not exist because he's traveled everywhere on the island and hasn't seen it. Piggy agrees that there is no beast on the island, but believes that the boys should examine the issue pragmatically. A littlun named Percival claims that he's seen a beast come out of the sea at night. Then, Simon attempts to tell the boys the true nature of the beast, but cannot articulate his thoughts. When it is suggested that Simon is trying to describe a ghost, Piggy grabs the conch and begins to protest. Jack steps in and insults Piggy. Ralph raises the conch to hold a vote on whether or not there are ghosts on the island, and the boys are silent. He feels the power of the conch weakening when the boys do not respond by voting. Jack begins to challenge Ralph's authority and says,

"Bollocks to the rules! We're strong---we hunt! If there's a beast, we'll hunt it down! We'll close in and beat and beat and beat---!" (Golding 91)

Jack leads his group of hunters away and dismisses Ralph and the assembly.

Ralph does not blow the conch and assert his authority after the boys follow Jack. He feels that if he were to blow the conch and have the boys disobey, then they would be complete animals on the island. Ralph then says that he wants to give up being chief. Piggy encourages Ralph to regain authority. Piggy wants Ralph to be chief because he knows that Ralph is his only protection from Jack and the group of hunters. Without civility and rules, the physically weaker members of society, like Piggy and Simon, will suffer.