I would say that your answer is hidden in the way you phrased the question.

The idea that revenge is bad is indeed liberal idealist bullshit. What matters is, as usual, the material reality of whatever the circumstances are. Will revenge being taken in the specific circumstances you're talking about end up doing more material harm than good? Revenge is not an inherently bad thing and it can be an extremely good motivating force behind very good and necessary actions. It can also be detrimental and end up harming people even in completely unintended ways, including the ones who are trying to enact their vengeance for entirely justifiable reasons.

It all depends on the situation. But I think we can safely say that revenge as an idea being either good or bad is a liberal-style framing or misunderstanding.