I too am appalled at the firing of the employee. A lot of businesses, not just Auto Zone have such policies. One store manager (not an Auto Zone) in Florida which has a good base of concealed carrying of weapons and a stand your ground law told me he has nightmares about gun fire erupting in his store.
He advised his store is a large cash generator and just any night he expected a robbery. He advised store policy was not to resist, try not to do anything to excite the robber and give the robber what they ask for.
He advised his great worry is a concealed carry will see the robbery in progress, and shoot at the robber, missing the robber and killing Mrs. X who was in the store shopping. The robber then opens fire killing the concealed carry shooter and a couple of other shoppers.
Then the civil suits would start over the deaths and the store not providing a safe “Shopping Environment” and the store manager just could not see how the store could win.
His reasoning logic was the robber would probably be apprehended, charged with murder and robbery but lacking two nickels too rub together, the store would be the one sued when civil suits started being filed.