why are people so...unpleasant?

Edgar Vargas is a somewhat religious man who was not afraid of Johnny C's threats to kill him, and talked to Johnny for a while--before he killed him. Johnny rather liked Edgar, despite killing him.
It is also believed that Edgar was supposedly meant as a lesson to Johnny, to teach him that not everyone in the world is as horrible of a person as he perceives them to be. But in the end Johnny ignores this 'lesson' and kills him anyway, not out of anger or hatred, but out of a necessity to feed the wall monster that controls him.