Atticus tells the jury that the state expects them to make three evil assumptions about Negroes: that they lie, are immoral, and cannot be trusted around women.
Atticus makes a full effort to defend Tom Robinson, in spite of the extreme racism present in Maycomb. At trial, he goes to great lengths to show that no crime even took place, and Tom Robinson could not physically commit the crime, and that Bob Ewell was the one who beat Mayella.
Yet Atticus knows he has an uphill battle to fight with the jury, because if they acquit Tom Robinson they are taking his word over a white woman’s. That is unacceptable. Atticus tries to remind them that they are basing their views on nothing but prejudice.
[The state has] presented … to you gentlemen… confident that you gentlemen would go along with them on the assumption-the assumption- the evil assumption- that all Negroes lie, that all Negroes are basically immoral beings, that all Negro men are not to be trusted around our women…(ch 20)
There are liars, and cheats, and people not to be trusted in both races, Atticus reminds them. In a court, a man’s skin color should not matter. In a court, all men are created equal.
Although Atticus does not get an acquittal, the jury does deliberate. The fact that they thought about it at all shows that Atticus made some headway getting them to question their assumptions.