Atticus knows he's stuck with the jury system of the period and that there is little that he can do to change it. He recognizes that members of the jury are not completely unbiased, especially when it comes to the color of a man's skin. He knows that no jury can be expected to take a black man's word over that of a white man, but otherwise,
"There's no difference between one man who's going to convict and another man who's going to convict..." (Chapter 23)
Atticus believes that most jurors are "reasonable men in everyday life," but that "people have a way of carrying out their resentments right into the jury box." Atticus knows that "Our stout Maycomb citizens aren't interested" or are "afraid" of serving on juries, leaving the selection to the less educated rural residents of the county. He believes that judges, not juries, should decide the fate of a man charged with a capital crime. But Atticus also recognizes that
"If you had been on that jury, son, and eleven other boys like you, Tom would be a free man." (Chapter 23)
Atticus believes the jury system works--it's just the individual jurors and "the secret courts of men's hearts" that get in the way of justice.