To Kill a Mockingbird

I'm not sure what you mean by rebelling against authority in the context of this novel, but disregarding social norms is a matter of personal belief. Rebellion against social norms is appropriate when those norms are oppressive, unjust, or devisive. Atticus took Tom's case because not to would have been morally wrong and unjust. The case against Tom was unjust, and the people of Maycomb who stood behind him rebelled against the norm.