Aunt Alexandra's ideas about breeding and family reflect her deep adherence to Southern social traditions and her belief in the importance of maintaining the Finch family's heritage and reputation. She values "good breeding" and is concerned about the family lineage and the Finch name. She believes that certain qualities should be preserved and passed down through generations, which includes adhering to social norms and expectations.
Atticus, on the other hand, is more focused on individual character and values. He believes in raising his children to be morally upright and compassionate, prioritizing their personal growth and development over concerns about family lineage or "breeding."
When Atticus tells them to "forget it," he is urging them not to argue or dwell on these differences in perspective. He recognizes that such arguments won't lead to productive outcomes and that they should focus on the more immediate challenges they face, such as the racial tensions and the trial of Tom Robinson.
In the context of the novel "To Kill a Mockingbird" by Harper Lee, Atticus's approach is portrayed as more morally just. He prioritizes individual integrity and moral principles over social expectations and family heritage. Aunt Alexandra's focus on "breeding" may be seen as reflective of the rigid and often unjust social norms of the time, which the novel ultimately challenges and critiques. Therefore, Atticus's perspective aligns more closely with the novel's themes of justice, equality, and personal morality.