This quote shows Scout's age, inexperience, and innocence.
We see this in Jem's response to her:
That's what I thought too... when I was your age. If there's just one kind of folks, why can't they get along with each other? If they're all alike, why do they go out of their way to despise each other? -Jem Finch, ch. 23
To me this quote shows this childhood ideal is still an ideal, but eventually is killed by reality. Harper Lee is making a very profound statement on the world - and speaking a very profound message. This message is, "Why can't we all just get along?" If these kids get it, why can't the adults?
But isn't that the sad reality? Kids do get it - the idea that it doesn't matter what we look like nor how much money we make, or even how educated we are - we can find something in common and love each other - and adults, too often, don't.
To me, this is a statement that shows one of the main themes of the book. It is meant to tell us that all people are the same -- that there are not (or should not be) black people and white people, rich people and poor people. There should only be people.
This is, as I say, one of the major themes of the book. Scout and Jem are encouraged to think of Boo Radley as a person, not a monster. Calpurnia makes sure that Scout does not treat Walter Cunningham like he is lower than the Finches. Atticus tells the kids they need to respect black people and even people like Mrs. Dubose.