One example of this comes during the children's constant attempts to "make Boo Radley come out." Although Atticus does not know about the gifts that Jem and Scout receive in the secret knothole of the oak tree, he does recognize that their actions are intrusive, and he orders them to "stop tormenting that man." Later, the children come to realize that Atticus is right; Boo's acts of kindness--mending Jem's shorts and warming Scout with a blanket on the night Miss Maudie's house burns--teach them that he is not a man to be feared, and they finally understand that Boo's self-imposed reclusiveness should be honored.
Another example comes during Scout's and Dill's talk with Dolphus Raymond. Scout tells Raymond that
"Atticus says cheatin' a colored man is ten times worse than cheatin' a white man."
Raymond agrees, telling her that Dill's crying in the courtroom stems from his crying
"... about the hell white people give colored folks without even stopping to think that they're people, too."
Atticus's own advice to Jem concerning it being "a sin to kill a mockingbird" can be interpreted in two ways: The killing of beautiful, innocent songbirds is sinful, as is the harmful treatment of the symbolic human mockingbirds in the story, such as Tom and Boo.
Throughout the novel, Atticus protects Tom Robinson from a lynch mob and defends him in front of a prejudiced jury. Atticus feels the responsibility to defend and protect innocent individuals and risks his health and reputation doing so. When the Old Sarum bunch arrives at the Maycomb jailhouse to lynch Tom Robinson, Atticus refuses to leave the scene and saves Tom's life. Atticus also knows that Tom Robinson did not assault and rape Mayella Ewell which is why he defends Tom to the best of his ability throughout the trial.
Another example that expresses the theme that individuals have a responsibility to protect innocent beings takes place when Bob Ewell attacks the children. Boo Radley heroically comes to the defense of Jem and Scout. Boo ends up killing Bob Ewell and protecting the innocent children. Afterwards, Sheriff Tate refuses to tell the community that Boo saved Jem and Scout's lives to protect him from the limelight. Heck Tate's decision to not portray Boo as a hero to the citizens of Maycomb depicts his responsibility to protect innocent individuals.