How does Montresor's understanding or lack of understanding influence the themes in "The Cask of Amontillado" by Edgar Allen Poe?

Revenge is an important theme in the story, and much of the plot hinges on Montresor's understanding of this concept. Montresor understands revenge, which he understands as striking back when you are injured, as follows: make sure to plan your revenge in great detail so that you are not caught, and make certain the person you are punishing knows it is you who are doing the punishing.
Montresor follows through very carefully on his idea of a just revenge. He makes sure no third party could look back and connect him with Fortunato's disappearance. He plays on Fortunato's vanity to lure him into a dark catacomb and keeps him drunk and off-balance the whole time they are down there. Montresor also makes sure his servants are out of the house so that there will be no surprise witnesses to his act. He brings all the supplies he needs to wall up his victim. At the end, he makes sure it is clear to Fortunato exactly what he is doing to him. 
Beneath the theme of revenge lies the theme of justice. Montresor plans and executes his revenge very carefully, but he does not seem to question whether his punishment is just. He never explains what Fortunato has done to him to justify such as fate. All Montresor notes is that he has borne a "thousand injuries." What are these injuries? Is any injury so heinous that it justifies leaving someone all alone in a cold, dark, moldy place to slowly die of starvation and dehydration? 
Montresor appears to have become so obsessed with revenge that he has lost any sense of proportion. He lacks moral understanding and a moral compass. Rather than fit the punishment to the crime or forgive and forget, Montresor lets his blind desire for revenge overtake his reason and compassion.
Because Montresor's revenge is so extreme and cold-blooded, we as readers are drawn to question the very idea of revenge and how anger nursed in silence can grow out of control.