For my English class, I need to write a critical essay that demonstrates the idea that hatred is a learned trait and is not born into a person.
As the older characters are far less shocked and hurt by the verdict in Tom Robinson's trial, we migth use this fact to help make an argument that hatred is learned. The children have not yet learned hatred, nor have they learned to expect it in their peers and community. This is evidenced by the tears shed by Dill and Jem as a result of the trial.
I think any of the major scenes of hypocrisy would help you prove this. Consider the scene in which Aunt Alexandra hosts the women of Maycomb for the "Missionary Society" tea. In one room, in one scene, many women display almost a learned ignorance and are wholly unaware of their hypocrisy. Also, Scout's first day of school does a good job of displaying the knowledge the children have of the societal "pecking order" in the town, of which Miss Caroline is ignorant. Scout's innocence in each scene helps prove that these lessons are so "natural" that the behaviors are not even considered unusual nor morally wrong.
I definitely believe this side of the question is harder to prove within the context of TKAM. However, another character to consider is Aunt Alexandra. Brothers Atticus and Jack are peaceful and both love their fellow man; this is not necessarily true of Alexandra, who categorizes people according to their family heritage. She hates the Cunninghams because they are "trash," and she refuses to allow the children to visit Calpurnia's home because, as a black woman, she is beneath the high status of a Finch.
Dill could also be used as another example. His parents continually disappoint him and brush him aside, yet he does not hate them. He loves them so much that he lies to make them sound better. He doesn't want other people to know how much they have hurt him. He doesn't want people to dislike them for the way they have treated him. If hating someone was innate, Dill would hate his parents.
Another example would be that of Boo Radley. Clearly his father and brother were less than tolerant of people and their faults. It would have been "natural" for Boo to have inherited such negative emotions as hatred and intolerance. However, his care, compassion, and concern are evident throughout his entire relationship with the children. Clearly, he has not learned to hate.
Mr Raymond Dolphus demonstrates that hatred of all Negroes has been learned by most of the townspeople, for he does not hate them; instead, the member of the gentry of Maycomb actually lives with them even though he has resided in Maycomb all his life. Also, because Mayella Ewell invites Tom Robinson into her yard and hugs him, there is an indication that she has no inherent hatred, nor has she learned such hatred from her father, Bob Ewell.
I think that this point is made most clearly through Jem and Scout. Atticus goes to great lengths to teach them how to treat all people fairly. If hatred were something that were innate to people, it would be useless to try to teach the kids not to hate. Instead, hatred (or the lack of it) is taught. This is why it is worthwhile for Atticus to try to teach the kids not to look down on others.