Why does Atticus tell them to forget it in To Kill a Mockingbird?
Another example of Atticus suggesting that Scout forget about advice she has been given in To Kill a Mockingbird comes after Miss Caroline has told her that
"Your father does not know how to teach."
Miss Caroline believes that the reading sessions that Atticus and Scout so enjoy should be ended. When Scout tells Atticus about this, he asks her if she knows what a "compromise" is. He then explains that if she will agree to continue going to school, they will continue to read each night--but without informing Miss Caroline of their agreement. The teacher might not approve of their "activities," he tells Scout, so it will be just their little secret.
Are you referring to Aunt Alexandra's ideas about family and heredity? If so, Atticus has no ingrained beliefs that family is essential to ones actions as an individual, or that heredity makes one person better than another. He truly believes that people should make up their own minds about who they are and their place in the world. As well, he has no racial bias and no belief that a white person is better than a black one. Atticus wants his children to believe in themselves for their own abilities - not for who they may have been related to.