If I understand your post, you are wondering why Tom Robinson is a target of racism in To Kill a Mockingbird. First, racism was a fact of life in the 1930s Deep South, and Alabama was no exception. Many white people considered African-Americans as second-class citizens, and they were treated as such. Segregation--in schools, churches, neighborhoods and virtually all public places--was firmly established. As for Tom, he was particularly despised because of the charge against him: the rape and beating of a white woman. The "N" word is used often to describe Tom: More than once, Atticus is called a "nigger-lover" for his decision to defend Tom. The prosecuting attorney, Harry Gilmer, repeatedly calls Tom "boy" while he is cross-examining him. Perhaps the most memorable racist quote concerning Tom comes from Bob Ewell when he testifies that he
"... seen that black nigger yonder ruttin' on my Mayella!"