I would have to say that, no, the revenge of the story is not acceptable for many reasons. Perhaps the biggest reason that the revenge here is so unacceptable is that we, the readers, are given no clear cut reason for the revenge. Montresor was wronged by Fortunato, no specifics, just "wronged"; it seems a little difficult to sympathize with Montresor, a murderer, or accept his actions, when there is nothing to go on. For example, if Fortunato had harmed someone Montresor loved out of some evil plot or plan to cause him pain, then you might be able to understand the revenge; however, even though understandable, it is still not necessarily acceptable. Basically, nothing makes revenge acceptable, but in some cases, revenge is more understandable than others.