Why does Ralph and jack both insist on going after the beast?

It speaks both to Jack's digression into savagery and Ralph's wish for a save civilization. Jack sees the beast as a chance to vent some of the savagery that he has turned to, and wants to use it as a way to prove himself and the rest of the hunting boys. Ralph sees the beast as a threat to the safety of the boys' world, and thinks that they have to fight it to stay safe.