If you’ve sufficiently dehumanized someone who’s harmed you in a major and who you justifiably hate, fucking them over can make you feel absolutely triumphant. I think there are four problems with revenge:

1. It’s inherently escalatory unless you’re really methodical and sneaky about it, which most people aren’t. Accepting revenge as a permissible response to being wronged can make you overlook other options that would help deescalate the situation or bring justice, especially if the wrong wasn’t that big of a deal.
2. The pursuit of it can be really unhealthy and pretty obsessive. It’s very much a way of consistently reinforcing rage and feeding it, so if you have the option to not do that, it’s probably best not to.
3. Dehumanizing anyone is a psychologically destructive act. Sometimes people don’t have a choice and not everyone deserves empathy from everyone at all times for all their actions in equal measure. But again, if you have a choice, dehumanizing people isn’t great for you.
4. You can be wrong. Simple as. You can be wrong about the perpetrator. You can be wrong about the act itself. You can be wrong about a bunch of things and taking revenge on someone who didn’t deserve it is just needless harm.