How does the narrator feel about revenge in "The Cask of Amontillado"?
In Edgar Allan Poe's "The Cask of Amontillado," the narrator feels that revenge is justified, particularly when one has been personally humiliated or in the event that a word or action endangers the good name of the individual or his family.
Notice that, according to the narrator, he had been hurt (verbally, we assume) "one thousand times" by Fortunato. He would put up with it, but then Fortunato apparently insults him directly. This is when the issue gets real for Montresor.
In Montresor's own words:
A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong.
Basically, what he is saying is that, for every wrong someone does to you, there must be payback. He is a vengeful man.
Hence, in the narrator's perspective, revenge is fair, justified, and necessary when the one thing that defined a man of his time, that is, his good name, is in any danger of being disrespected or has flatly been disrespected by someone else.
Another thing to note is that Montresor's family's coat of arms and motto are quite telling:
"A huge human foot d'or, in a field azure; the foot crushes a serpent rampant whose fangs are imbedded in the heel."
The family motto is as follows:
"Nemo me impune lacessit." This can also be understood as "Nobody provokes me with impunity."
All of this tells us that Montresor is a man who would have taken revenge no matter what the offense may have been. He has a fixation for retribution in his head, and it is clear that his family shares the same point of view.