Oh, I don't think the "do unto others" thing is a good idea, but I have heard it suggested. Whatever is done, it cannot be vengance, but either punishment (with the opportunity for the person to rehabilitate) or putting the criminal away from society because they are too evil and are deemed as someone who can never change.

But I have to admit that I'm not at all sorry that Paul Harris, Idi Amin, Heinrich Himmler, Pol Pat, and similar sorts are dead from whatever reason. They're not the sorts I'm missing.