Like most of Steinbeck's modern paradoxes, the role of human beings in the novella brings out the source of modern consciousness' greatest hope with a simultaneous revelation of the greatest of hazards.  The characters in Steinbeck's work represent the capacity for some of the most tender interactions with other human beings, but also for some of the worst and most brutal treatment of them.  Consider George as one such example.  He has nothing but love for Lennie.  He cares for Lennie, looks out for him, and shelters him when difficulties emerge.  Yet, this very same characterization has to be set against the moment when he told Lennie for a joke to jump in the river only to see him near drown.  It is also this very same constitution that enables him to shoot Lennie in the back of the head at the end of the story.  The capacity for love and tenderness stands next to the vision of the most awful of actions.  Consider Lennie, himself, as another example of the paradox of both hope and hazard.  Lennie has a child- like love for animals.  His love of mice, pups, and, of course, rabbits are all an example of this.  Yet, his force of touch, the strength within his hands, kills all of said animals.  The capacity for love and tenderness is offset by the strength he possesses, a hazard for such small creatures.  It is this same paradox that causes him to end up killing Curley's wife, a paradoxical moment in that Lennie wants to touch something beautiful and when he does he ends up killing it.  In both George and Lennie, Steinbeck's paradox of human beings being the source of both the greatest of hazard and hope is evident.  In the end, human beings become cursed figures, but Steinbeck realizes that this is "what's eating" at human beings.  When Carlson calls out "what's wrong" with "those two," it might be because Silm and George are aware of this paradox, a condition in which humans have to become their only hope from their own penchant for destruction.  It is something that causes weight upon the human being, and something that must be reconciled or at least accepted.