“When a character acts selflessly against the prevailing vice(s) of the
dominant social order, true virtue exhibits itself.”
Tom Robinson acts selflessly simply by being such a generous man to help Mayella Ewell whenever she had tasks for him to do. It was against the dominant social order because racism was so dangerously popular. He was risking his life by stepping over the property line, but acted selflessly to be a gentleman to a lady in need. He would help chop up furniture, reach things too high for Mayella, and fix little quirks of the house. Tom seems very sure of how kind his is trying to be, he values his ability to be of assistance quite high. These acts get to people as they realize that true virtue is valuing everybody the same, no matter what skin colour.
Boo Radley is in a completely different situation, as pretty well the whole social order is against him and the rumors direct unsupported blame on his innocent head. When he goes out to save the children he knows the risk he's taking as he enters the social world as an unacceptable being. But he also knows it is the right thing to do. "True Virtue" presents itself as he successfully saves the children's lives and shows the town he's got a good heart.
Atticus Goes against the social order in such a brave way, it is mistaken as a bad thing. Standing up for a black man was such a wrong thing to do, and a waste of time according to the people in Maycomb. Though he was showing real bravery, the town thought him a coward for helping a man of another race. He effectively proves the white man to be in the wrong at this hearing. Though it doesn't save Tom's life, it shows everyone who attended the court case, or later heard about it, that black men do have good hearts, and are only as wrongful as the rest of us. Humiliating Mr. Ewell is at the surface, but the value and increase in equality lies not much below it. The dominant social order begins to get a clue.
