Note Slim's comment about everyone being afraid of one another, and Curley's wife's reference to them all being scared of each other
I don't think it is. One of the unspoken tragedies of the Great Depression was that it reduced men to doing what ever it took to survive. It alienated and distanced them from their families, and from each other. So it was less about fear for what would happen to another person, and more about fear of an uncertain and economically grim future, full of job insecurity and poverty.
Given that Steinbeck writes from a Naturalistic perspective, the novel Of Mice and Men is written from a scientific aspect (a main characteristic of this genre). In Naturalism, the author looks at his text as an experimentation in human behavior. Therefore, I do not believe that Steinbeck uses fear as a main theme of the novel. That being said, one could look at the fear instilled in the ranchers because of their innate will to survive (another aspect of Naturalism). I think that Steinbeck uses fear to highlight the natural conflict that exists between man.
Another major fear a reader might infer is the fear of being unable to escape the inevitability of man's nature. Despite George's relationship with Lenny and his efforts to minimize the impact of Lenny's inability to control his inappropriate responses, George ultimately fails Lenny as he cannot prevent the tragedy that occurs with Candy.
Post #2's observation about the men's fear of the intrinsic nature of man to be cruel is very astute. For, the more insecure a man is, the crueler he will be to others. In the time of the Great Depression, men reverted to the basics of Darwinism. And, as bretthe points out, the characters as ones with weakness are apprehensive about their chances in the struggle to survive.
I think that the fear of sharing oneself too much, of being too close to others is also part of the issue which makes some characters reject others and some crave their attention.
Curley knows that his wife sees through his cocksure facade and is not impressed with his need to prove his masculinity. This is why he seeks out combatants to help him assert his power. Curley's wife is in turn rejected and, desparate for love and intimacy, she tries to engage the attentions of others.
Candy has turned his world inwards and shares only with his dog. When Carlson shoots it, Candy turns to George and Lennie to ease his loneliness.
Slim observes others, and yet becomes close to George; understanding his reasons for shooting Lennie and escorting him away after the killing.
Crooks is excited at the visit of Lennie and realises that there is no risk in befriending Lennie and sharing secrets as Lennie will never remember them to reveal them.
Part of George's motivation in killing Lennie could be said to be the fact that he may be implicated in Lennie's killing of Curley's wife, and it is at this time that he needs to be free of his friend lest he should betray both of them.
I think what people fear in this book is being powerless and unimportant. You can see this in a lot of the character. George wants to have independence--power and control of his own life. Curley wants badly to be important, a big man. His wife wants to be an important movie star. They all fear having no power to control their lives.
^ Good answer :)
I am studying this right now, and believe that the main concern is not the fear for another man, but in fact the fear of the human character (i.e. mankind).
Each character is burdened or crippled in one way, and the main focus of the novel is to reveal how this not only creates fear, but reveals the cruelty of the human character.
For example, the killing of Candy's dog generates an enormous amount of fear in Candy. As the men kill the dog that they feel is now useless, Candy comes to realise that he could possibly become a victim of age discrimination, and could be asked to leave the ranch.
Every other character has their own flaw; in short:
Lenny - mentally challenged
Curley - Ex-fighter with no recognition
Curley's wife - Trapped in an unhappy marriage and isolated by her husband
George - Carrying Lenny's Burden
Thus, it is not fear of another man, but the fear of a man's fundamental character that people fear. The fact that humans generate cruelty from their own weakness (essentially bullying) is a shocking revelation and is eventually what all the characters fear, and what shatters their dreams.