To refute is to essentially prove something false or unreasonable.
One way that Harper Lee refutes this prejudiced attitudes toward blacks is through her character of Dolphus Raymond. Coming from a land-owning family affords Mr. Raymod some affluence within Maycomb. Lee chooses, however, to put a spin on the character of Dolphus Raymond by having him choose to live with and have children with a black woman. This choice disgraces him in the face of many people in Maycomb,as they subscribe to the more prejudicial beliefs of the time period. Dolphus refutes this prejudice because he CHOOSES to live his life with a black woman, and he is happy living it. He even goes so far as to pretend he is a drunk so that others will have a justification (in their minds) as to why he lives that way. He is making fools out of all those with their prejudicial beliefs.