Set in the 1930's Depression era, this novel expresses through Slim the struggle of people for simple human decency in the face of so much meanness and ignorance in the world. Slim admires George's friendship with Lennie because no one ever "seems to give a damn about nobody". Slim confirms the cruelty of the world they live in when Carlson wants to kill Candy's sick, old dog, expressing the belief that the weak of the world have very little hope of protection from those who would take advantage of them. This belief is also shown when Slim drowns four of the puppies his dog has because their mother couldn't have fed all of them.
Overall, people who are powerless or handicapped in one way or another are considered to be undeserving of protection or preservation in society. This underscores the "survival of the fittest" theory where only the strongest people in a society will survive. During the Depression, resources were limited, and the powerful felt it was irresponsible to "waste" resources on those who were weak or handicapped.