In To Kill a Mockingbird, Harper Lee uses the fictional narrative of Tom Robinson to bring attention to systemic racism in United States. She also uses the book to bring attention to the hyper-criminalization of Black men and the marginalization of the poor.
Recall how there is a clear lack of evidence in Tom Robinson's trial. The Ewells also present conflicting testimonies. Such inconsistent accounts are technically not enough to convict a person, not to mention that they also suggest that Tom Robinson is innocent. However, the jury finds Tom guilty. If Tom had been a white man, he likely would not have been convicted. Lee uses this blatantly unjust case to highlight the destructive influence of racial discrimination. The way the white men in the town also try to lynch Tom shows how racism provokes violence and hatred.
In addition, Lee also uses the plight of families like the Cunninghams and the domestic violence in the Ewell family to highlight the destructive impacts of poverty on people's lives. These stories about racism and poverty are meant to make readers aware of and upset by these social issues. In doing this, Lee urges readers to take action to combat these problems.