Prejudice is part of the reality of the culture of Maycomb.
Comprising the main portion of the book's examination of racism and its effects are the underlying themes of prejudice vs. tolerance: how people feel about and respond to differences in others.
Beyond racism, prejudice is seen in the class distinctions and judgments made relating to race and gender. We see this in the case of the Ewells as well as in the ways Scout is treated for her choice of clothing and behavior.
The courthouse embodies and formalizes a number of these generalized or categorical biases. Women are not allowed to sit on juries. People of Maycomb are unqualified, uninterested, or unwilling to sit on juries due to a number of factors, including a sensitivity to offending the values (and prejudices) of neighbors.
Above all else, racism is the prejudice most clearly on display in the courthouse situation. It is here that Jem and Scout learn hard lessons about how deeply entrenched certain cultural biases are in Maycomb.
The town is exposed to the reader as being far from innocent, but rather a town riddled with bigotry, hatred and injustice.
Outside of the injustice and prejudice of the verdict that convicts Tom Robinson wrongfully of rape, the courtroom situation also depicts other elements of presumption and prejudice. African Americans are made to sit separately from others in the court house. Dolphus Raymond also reveals the fact that he has developed an elaborate ruse in response to the town's biases.
He fosters a reputation as a drunk to give townspeople a reason to excuse his flaunting of social taboos.
For Raymond and the situation of the courthouse, no personal rules of interaction or individual mandates regarding prejudice are expressed. The prejudice of the town is, indeed, institutional and impersonal, though not universally accepted.