I think there's just one kind of folks. Folks.
It’s another powerful moral given to readers in Chapter 23 through the conversation between Scout and Jem. Scout is offended that their aunt forbids him to communicate with Walter, calling him trash. Jem tries to explain Scout that there are different kinds of people and Walter doesn’t belong to their group, he almost can’t write and read and isn’t as intelligent as they are. So their aunt is worried that meetings with people from inferior group can have bad influence on Scout. But Scout responses with logical answer that no one is born knowing how to read and write, Walter just had no chance to learn it. She concludes her speech with the quotation above, proving her point and leaving Jem angry but without arguments. After that Jem bitterly says that he used to think that way too when he was Scout’s age and Boo Radley isn’t so wrong staying inside, away of this unfair world.