How is the rabid dog a symbol of racism in "To Kill a Mockingbird"? What relation is the courthouse to Atticus?

The rabid dog is a symbol of the racism that is in the town.  Racism, like the disease of rabies, will continue to spread unless it is "shot" down in its path.  The rabid dog will also become sicker and sicker until the disease destroys the dog's body, causing paralysis and eventually, death.  That is what racism does, it paralyzes growth in a community and will destroy any semblence of that community in its wake.  Atticus' quiet strenth that Jem and Scout witness and were previously unaware of, his ability as a sharp shooter, eradicates the rabid dog, as he tries to do with the racism in the town by trying to give Tom Robinson a fair trial.

The courthouse, as a symbol of Atticus, is the quiet strength that would hopefully be the backbone of eradicating racism in the town.  Atticus is intent on giving Tom his day in court to prove his innocence in front of both the white and black members of the community.  The races are separated upon entering the courtroom; this was commonplace for the setting of the novel, however, the black people are seated in the upper tier of the courtroom.  Perhaps we can see this as an elevation of the statis of black people to come, something that Atticus has done in his appropriate defense of Tom.