How does John Steinbeck show the way society treats people in Of Mice and Men through his characters?

In Of Mice and Men, Steinbeck uses his characters to show how society treats people. Lennie Small is mentally challenged. He often makes wrong decisions due to his childlike qualities. He unintentionally harms animals and people due to his childlike desire to pet soft, furry animals. He also is fascinated with soft textures. He is on the run because he touched a girl's dress. He would not let go and the people accused him of trying to harm the girl. He was just interested in her dress fabric, but society interpreted his actions as dangerous to the girl.

Lennie's mental disability is a frowned-upon handicap by society during this time. Lennie has no friends except George and Candy, and George has also been mean to Lennie by playing dirty tricks on him from time to time. Also, Curly is abusive to Lennie because he takes pride in ridiculing him. Curly likes to bully people. He tries to take advantage of Lennie's slow abilities.  

Mentally retarded people always bring out the sadistic potential in certain types of boys and grown men. George himself used to play dirty tricks on Lennie just for meanness.

Crooks is a black man who feels superior to Lennie because of Lennie's mental disabilities. During this story, blacks were inferior to white people. Picking on Lennie makes him feel superior. 

Crooks is at the bottom of the social ladder on the ranch because of his race and his broken body. But he sees in Lennie an inferior who could make him feel one rung higher. 

Because Lennie is so strong, he often unintentionally harms people and animals. He means no harm, but society treats him as if he is an abusive person. When Lennie accidentally breaks Curly's wife's neck, Curly is determined to hang Lennie. Society has no mercy on Lennie, even though it was totally an accident. 

For this reason, George knows he has to shoot Lennie before Curly can find him and torture him. Curly does not care that it was an accident. He has no understanding for Lennie's disability. 

Steinbeck reveals the views of society during this time through his characters' actions and dialogue. 

Steinbeck was a realist. His characters show good and bad qualities, and many of them change, as real people must do.