I think revenge is good; it's the way it happens is what is questionable. In my own life, I have found that when someone has done me wrong they always get what's coming to them. It happens even if I never have a role in them getting it.
Real life example ...
I had this chick friend that I used to work with and party with on the weekends. Slowly after she burned me at work, literally, our friendship started to break apart. The real head turner that broke us apart was ridiculous and un-called for. What happened was that she was having a get together with a bunch of people and our mutual friend called me up to the party and demanded my presence. I, myself, being a usual patron of the parties at this girl's house obliged and drove over to the house to see everyone. Well, the host was out and the girl that invited me over had to step out to pick up some take out. So, I chilled out at the house with everyone until the "hostess" arrived. When she walked in she took a look at me and with a sarcastic tone of voice welcomed me and asked me what I was doing there. I let her know that I was invited by our friend and she proceeded to throw an immature fit for a 24 year old about how no one asks her if they can come over and made a spectacle out of not only herself but me as well. She humiliated me while she was in the other room. So, I texted my other friend to prepare her for the news and to let her know that I was silently stepping out to go where I was welcome.
So, revenge you ask? Well, I'm pretty passive about getting back at other people because you never know when it'll get back at me. A lot of legal ratifications go into revenge these days. People are sue happy.
It's not the first time that this "woman" has just tossed people to the side like they weren't worth the same rights as other people. I guess she had built up a lot of bad "karma" you might say.
What's her punishment? Well, recently she was out joy riding with some of the people in her life that she has chosen to keep around for a lengthy period of time for whatever reason she has to use them. Joy riding on four wheelers. She was riding with a passenger and going pretty fast and hit something while riding. She was thrown into the air and hurled into a creek stream. Something entered her body and punctured a lung. She's been in the hospital in intensive care for some time now.
My point is that you don't have to sully your own hands on behalf of revenge. It only makes you feel like a bad person just like they are. If you're patient and have a heart that allows you not to dwell on the bad things that people have done to you, you will see in the long end that their own misdeeds will catch up to them somehow, someway.
So, my friend. It'll be okay. Just remember that if they really have done something so bad to you, you no longer have to keep them in your life. Out of sight, out of mind. It'll be off your immediate memory soon enough. You'll forget all about it and live you life again with happiness. Sure, you'll remember it in the future from time to time but each time you remember it, you'll care that much less in the future each time.