Curley and Carlson of John Steinbeck's Of Mice and Men represent the alienated men who become brutish and cruel as a result of their separation from friends and family with whom they can empathize. Alone and among strangers, these men lose the sesitivity that comes with sharing with others. As a socialist, Steinbeck believed deeply in the importance of the brotherhood of man; he felt that left to his own, man becomes heartless, cruel in his fear of others in their lonely vulnerability.
Thus, Steinbeck's motif, the strength to oppress others is itself born of weakness, is again interposed in the final scene that sees the cruel and alienated men, Curley and Carlson, asking what is wrong with Slim and George with ridicule in their tone. They understand nothing of the fraternity of men; they have lost their very souls to the cruel circumstances of the isolated ranch and the alienation of the itinerant worker in the Depression era. They are but brutes; the one always ready to fight, the other ready to shoot old dogs. Much of their humanity has been lost in the mouse maze of life in which they live, going from lonely place to lonely place, whether it be a new location or to lonely home and unfriendly bunkhouse, as is the case with Curley.
At the end of the book, Curley and Carlson watch George and Slim walk away. They wonder what is wrong with the two of them -- why they seem so upset. This really shows that Curley and Carlson are unfeeling and cruel people.
This is in total contrast to Slim. Slim understands why George is sad. He is sad because he had to kill his best friend, who was a a decent man. Carlson, by contrast, pushed Candy into killing his dog. He has no idea about how other people feel and he really doesn't care. His last words show that he and Curley really do not understand or care about people and their feelings.