I believe they are common because people believe that is where we could be headed. Will we run society into the ground, or will we prosper? Will the society be a "Divergent" or "Giver" society or will it exist as it does today? Since we have no way of knowing, we pretend we do.
Can you please explain your question better?
Beowulf tells Hrothgar that he will fight Grendel with his bare hands, as Grendel doesn't fight with weapons (it seems he can't even be killed with a blade). The only help Beowulf will get is the help of his warriors. Beowulf is aware that the lives of all his warriors are at stake, and anticipates that Grendel will eat them if they fail, but he is still eager to do this. This reveals that the leader is always the first one to fight, in front of his followers. But although he vouches for their lives, they must follow him to death, if need be.
Just like Beowulf is a leader to his warriors, Hrothgar, as a king, is the spiritual leader of the realm. Beowulf yields to him and wants to fight and even die for him, as Hrothgar represents the God's will on Earth. When the realm is physically endangered by a murderous, devilish villain, it means that the God's order on Earth is symbolically endangered, and it takes a hero to restore it.
