I don't really subscribe to it. If someone does something ugly to you, it's because they have ugly in their heart and are probably an unhappy person. In order to seek revenge you have to let that ugliness into your own heart, thus making you unhappy. Hell, just being angry at someone for an extended period of time makes me sick in my stomache. After it's all done, you now are in the position of either standing there realizing you did something horrible and feeling like crap or you realize you did something horrible and feel good about it, which in it's own way should make you feel like crap. In short, they are them and you are you. They did something horrible because they are horrible. Even if they deserved it, why would you do something horrible?