Atticus did not volunteer to defend Tom Robinson, nor did he really wish to take on the case of a black man accused of raping a white woman. He told his brother, Jack,
"You know, I'd hoped to get through life without a case of this kind..."
Atticus knew such a case would make enemies in Maycomb and, possibly, even cause trouble for his family. But he believed that he had no choice when Judge John Taylor assigned the case to him instead of a public defender. Judge Taylor must have realized that Tom would receive the best defense possible when he
"... pointed at me and said, 'You're It."
Atticus decided to accept the case because he knew he wouldn't be able to look his children in the eyes if he did not.
"... do you think I could face my children otherwise?... I just hope that Jem and Scout come to me for their answers instead of listening to the town... I hope they trust me enough..."