The children were somewhat disappointed with their father. He was old and boring. Then he shot the rabid dog in one shot, and they admired and respected him.
Our father didn't do anything. He worked in an office, not in a drugstore. Atticus did not drive a dump-truck for the county, he was not the sheriff, he did not farm, work in a garage, or do anything that could possibly arouse the admiration of anyone. (ch 10)
The children are also disappointed that Atticus wears glasses and cannot see well out of one of his eyes. He is considered positively feeble, and not as interesting as other dads. He does not have a glorious job. All Atticus does is read, and he does not “play poker or fish or drink or smoke” (ch 10). He seems tame.
Unfortunately, he also “would not remain as inconspicuous” as the children want him to. His defense of Tom Robinson is troublesome for the kids, because it causes much taunting by other kids and adults.
When a rabid dog threatens the town, Atticus and the sheriff are called out to face it. Unfortunately, the dog is so dangerous it has to be taken out in one shot. Heck Tate the sheriff knows he can’t do it from a distance.
"For God's sake, Mr. Finch, look where he is! Miss and you'll go straight into the Radley house! I can't shoot that well and you know it!" (ch 10)
Atticus has not shot a gun in years, but he does not hesitate. He drops the dog.
Atticus’s shooting the dog is a demonstration of his courage, but also of his symbolic importance to the town. Just as Atticus killed the mad dog to save Maycomb from rabies, he is defending Tom Robinson to save Maycomb from racism.