How does Harper Lee in To Kill a Mockingbird use Atticus to show that compassion is the only proper response to "mad dog" behaviour, so as to help his children grow in compassion themselves?
The "simple hell people give other people - without even thinking" is evident throughout the novel and would like to focus on specific example in the text where Atticus guides his children towards compassion.
Atticus demands that his children stop "tormenting" Boo Radley in the early chapters of To Kill a Mockingbird, and his reasoning has to do with the compassion that he feels--and that he wants his children to feel--for the misunderstood Boo. The children eventually come to learn that the stories they have heard about Boo are not true--that he is no monster--from the gifts they receive from him in the knothole of the tree. Boo's mending of Jem's pants and Boo's later act of placing a blanket on Scout's shoulders on the night of Miss Maudie's house fire further shows the children that Boo was their friend. They finally come to accept that if Boo didn't want to come out of his house, then it was his right.
I sometimes felt a twinge of remorse... at ever having taken part in what must have been sheer torment to Arthur Radley...
After Boo saves the children's lives on that fateful Halloween night, Scout realizes that
Boo was our neighbor... But neighbors give in return. We never put back in the tree what we took out of it: we had given him nothing, and it made me sad.