In Harper Lee's To Kill a Mockingbird, I believe that the idea of "all men are created equal" is something that Atticus struggles with.
Atticus feels that all people are equal morally and under the law, and that skin color and one's heritage should have no bearing upon the value of the individual.
However, Atticus struggles with his community's perceptions of equality. Atticus' morality will not accept how his peers treat those who are supposed to be "equal."
In Maycomb, the town in which they live, some people consider themselves more equal than others. The whites of wealth and property consider themselves superior to those whites of the lower classes, and don't consider blacks to be human beings at all.
Ironically, Bob Ewell believes, even though other whites consider him "white trash," that he is far superior to Tom Robinson and his "kind" because Ewell has white skin.
All the little man on the witness stand had that made him any better than his nearest neighbors was, that if scrubbed with lye soap in very hot water, his skin was white.
As Atticus tries to see the individual rather than, for example, skin color or social status, he is disappointed with those tied to the past (the Civil War) and societal expectations (upper vs. lower classes), and their use of these things to judge the value of others. Equality is not subjective, nor are there different kinds . Atticus would see the concept of equality open to all people.