Interesting point about Tim Johnson and Tom Robinson. I think the argument could also be made that Atticus deals with the senseless but dangerous rabid dog in much the same way Scott deals with the ignorant and dangerous crowd. They both used the weapons at hand to diffuse a dangerous situation.
I would also like to make one comment about number 4 in k-pope's answer. We are told in the novel that Tom is shot trying to escape; however, there is evidence that he never tried to escape.
1) The only 'eyewitnesses' to his escape were the white guards who shot him and then reported the attempt to escape. White members of the establishment have already shown themselves to be unrealiable witnesses.
2) Atticus always said they would lose the trial, and Tom knew it. Atticus believed they had a chance of freeing Tom on appeal where judges were more likely to consider the evidence instead of the emotions. So, knowing that he would likely be freed on appeal, it makes no sense for Tom to try and run for it before the appeal took place.
3) Tom injured that arm in a cotton gin, one of the main reasons he could not have attacked Mayella. It's an equally good reason why Tom would not have tried to climb a fence to escape from armed guards.
4) The symbolic connection between Tim Johnson (rabid dog) and Tom Johnson are very clear. Both are lame on one side and perceived as a threat to society. Just as Atticus shot the dog to protect society from a rabid animal, the guards may have shot Tom to protect their society. In my class, we have a large discussion about whether the guards believed that Tom was a rapist or whether the idea that a black man's word is better than a white woman's was just too large of a challenge for a racist society.
"To Kill A Mockingbird" is a story centered around the trial of Tom Robinson, a black man accused of raping a white woman, Mayella Ewell. In order, the five major events that occur are: 1.) The children (Scout--the narrator, Jem--the older brother, and Dill--a boy who visits in the summer) dream up ways to have Boo Radley, the reclusive next door neighbor who few have seen, come out of his house. 2.) Atticus (the father) is chosen to defend Tom Robinson in the trial against Mayella Ewell. Scout and Jem stand up for their father when other children tease them about having a "nigger-loving" father. 3.) Scout, Jem, and Dill sneak out of the house and persuade a mob of people intent on lynching Tom Robinson to see the situation from Atticus' and Tom's perspective. 4.) The trial occurs. The children watch from the colored balcony. Tom is convicted and subsequently is shot and killed while trying to escape from prison. 5.) Bob Ewell, Mayella’s father, vows revenge on Atticus and attacks his children at night on their way home from a school Halloween pageant. During the struggle, Jem breaks his arm, and Boo Radley rescues the children—carrying Jem home. Bob Ewell is discovered dead and the sheriff convinces Atticus that Bob fell on his own knife. Scout walks Boo home, and as he disappears into his house, she wonders what life is like from Boo’s perspective.