Is the world portrayed in To Kill a Mockingbird by Harper Lee a fair one?

The world that Harper Lee portrays in her classic novel To Kill a Mockingbird is not a fair world where people are treated equally and justice is administered fairly. The novel is set in the small town of Maycomb, Alabama during the 1930s, which was a time when southern states enforced Jim Crow laws. Jim Crow laws imposed racial segregation, discriminated against black citizens, and severely limited the civil rights of black people.
In the small town of Maycomb, Alabama, Scout's father, Atticus Finch, is given the difficult task of defending a black man named Tom Robinson, who is falsely accused of assaulting and raping Mayella Ewell. Atticus and his children are criticized and ridiculed by their racist neighbors for his decision to defend Tom Robinson, and their well-being is even jeopardized in chapter 15 by a lynch mob. In addition to portraying the extent of racial discrimination in the South, Harper Lee depicts the destructive nature of racial prejudice during the Tom Robinson trial, where Scout, Jem, and Dill witness racial injustice firsthand as Tom is wrongly convicted by prejudiced jurors simply because he is a black man. Tom's wrongful conviction is the most prominent example of injustice and unfair nature of Maycomb's society, as well as a critique of the Jim Crow South.

No, not at all. The world portrayed in To Kill a Mockingbird is deeply unfair. In common with much of the South at that time, racial prejudice is rife in Maycomb. African Americans aren't treated equally and are subjected to official discrimination. The criminal justice system is stacked against them, as we see in the case of Tom Robinson. Tom's convicted on a trumped-up charge of rape and assault, despite there being absolutely no evidence whatsoever of his guilt. He's been convicted purely and solely because he's an African American and his accuser is white.
But Maycomb is unfair in other ways too. With such a small town mentality, this is no place for an outsider, anyone a little different from the norm. A good example of this would be Boo Radley. The townsfolk have turned him into a scary boogie-man on the basis of gossip and hearsay. And yet he ultimately proves himself to be a kind and gentle man, a complete contrast to the terrifying urban legend spun by ignorant gossip-mongers.