Atticus has Jack get guns for the kids, but refuses to teach them to use firearms, or air rifles. He say that Jack's job. Why would Atticus not want to pass on this skill?

Atticus is a man that detests violence. While Atticus knows that guns themselves do not make people violent he understands their symbolic power on kids. Atticus recognizes that Scout and Jem have plenty of time to be exposed to items like guns. The innocence of children is a valuable thing in a dark and violent world. Atticus recognizes that guns will be an inevitable part of their lives but would rather have them linked with another adult who is just as responsible as he is. The irony is that Atticus is quite handy with a rifle (the rabid dog incident) but this is as far as he wishes to be connected with symbols of destruction.