If you watch the whole novel as a representative book of American Culture, you strongly can see that basically every person is afraid of going in depth. How did Curly react on Lennie's act of killing his wife? In my opinion he acted very raging and upset. He made the decision right away to look for Lennie and kill him ("Curly wanta get him lynched", p. 94). I would take this as an example of not reacting in-depth and looking at all aspects of an issue. But what does this have to do with George's Motives to kill Lennie?
Be honest: How many choices did George really have? For stating the situation: A person called Lennie is committing an unwanted crime on a loved person that has the affect of making the husband raging. Lennie hides, and the husband comes after him with a rifle with the will to kill him for this act. George finds it out and is automatically involved with this situation although he hasn't done a thing. And now he has to make a decision for someone who is not able to understand that he can't make any.
The first possibility for George would have been, as it also happened in the book, to kill Lennie before he is being killed by Curly, the husband of Curley's wife. But there the question of moral comes up where you ask yourself it that really makes sense to kill somebody you love. In this case it definitely does. George thinks all the other situations through and sees that this is the only valid one. He has to think of himself too: He doesn't want to live a life of persecution, and his friends are