Steinbeck was a champion of the underdog and those who were considered second class citizens of that time: disabled, African-Americans, women, working classmen (laborers) and elderly. He treated his characters with gentle humanity and valued what they had to say. For example, in OF MICE and MEN Lennie is mentally disabled and without a family. George takes care of him and Lennie is portrayed as sensitive and loyal. Readers side with Lennie when characters such as Curley treated him with disrespect. Then there is Crooks who represents the inequality that African-Americans received at that time. He is forced to live in the barn to take care of the horses. The men don't want him to come in the bunkhouse because they say he stinks. Ironically, he becomes disabled because he is kicked by a horse and then receives the nickname Crooks. Disparate treatment causes him to feel lonely and isolated in society. Then there is Curley's wife who is never given a first or last name in the story. She is thought of as Curley's property and she does not have a say in her own destiny. The reader feels her pain when they hear of her broken dreams of stardom. Possibly she is not able to attain her dreams due to the sexism in society at that time and the mistreatment that she receives from her husband. Then there are the laborers who are depicted as men who are strong and worth being admired. For example, Slim is described as "majestic" and thought of as having integrity because he does not repeat what others say. Finally, there is Candy who is a senior citizen. Unfortunately, elderly people are still treated with some unjustice, however, Steinbeck allows him to dream by having him get excited about co-ownership of the farm. Since Steinbeck depicts his characters with openness and honesty, the reader is able to face their own sexism, ageism, racism and classicism. Steinbeck provides the argument that we all share the human condition of wanting to dream and have companionship. At the end of the day we are more alike than we are different.
Steinbeck wrote about what he saw. Honestly. During the Great Depression, he wrote about poverty and displacement. During World War II, he wrote about the war (The Moon is Down.) That honesty was upsetting to many people who preferred to think of America uniformly as "the land of free and the home of the brave."
The socio-economic status of those displaced by society, either by our government or by others, was something Steinbeck would repeatedly address in In Dubious Battle, in Tortilla Flat, The Grapes of Wrath, Of Mice and Men and beyond. Although he was repeatedly accused of being a communist, nothing could be further from the truth. His novel In Dubious Battle is a scathing indictment of communism. Furthermore, Steinbeck worked tirelessly as a war correspondent during the Vietnam War and was a speech writer for presidential candidate Adelai Stevenson. His love for our country is more than evident in one of his last published works, a non-fictional account of his cross-country travels, Travels with Charley. Despite all of evidence to the contrary, however, Steinbeck continues to be branded as anti-American for his scathing criticisms of the treatment of our citizens, especially in The Grapes of Wrath.
Steinbeck is also controversial because of his adamant refusal to "keep writing The Grapes of Wrath." Despite its inflammatory premise, booksellers didn't mind cashing in on its popularity in the least. They were less than thrilled when Steinbeck refused to churn out any more novels like Grapes. Instead, Steinbeck insisted on taking on new forms and themes.
During the period in which Steinbeck wrote, there was a huge push to unionize in order to protect the rights of people, especially those who may be underprivileged. Unionization was a large part of the novels "In Dubious Battle" and "Grapes of Wrath". Many Americans considered unions to be communist, and Steinbeck was often dubbed a "commie" or a "red". Steinbeck spent much of his life traveling up and down the California coast in search of work, and he understood the difficulties the lower class faced. This understanding is reflected in many of his novels, including "Of Mice and Men", and by advocating for the under-privileged Steinbeck was touted as controversial.
John Steinbeck wrote about underprivileged populations--groups of people who hard tough times surviving and would sometimes resort to any means necessary. Literature is a reflection of ourself and our society. Many people don't like to be reminded of the unpleasant sides of our societies, especially when there's no easy solution for these people.
Another consideration is Steinbeck's motive. Many people don't appreciate when artists use underprivileged groups for their artistic value.