Why did Atticus accept the Robinson case?

Atticus accepted Tom Robinson's case because he knew no
one else would want to take the case, and if anyone else did, he wouldn't put on a good
case or care whether Tom was convicted. Atticus knew the odds of getting Tom off from
the very beginning, but he knew that he had to try. Taking these "baby steps" was the
only way that racial bigotry was ever going to change in the South. Atticus knows Tom is
innocent, and if Tom was white, he would have been found innocent with the evidence
Atticus presented. Atticus at least made the jury deliberate for a while before bringing
in a guilty verdict.