I think hoping and praying for someone to 'get theirs' is the same is taking revenge on someone. A philosopher once said that before you set out on a journey of revenge, dig two graves. People who focus on someone else's bad behavior and worry about whether they will be punished are only hurting themselves, in my opinion. I prefer to ignore people who behave badly. I can't control what they do; I can only control how I react. I prefer to focus on what I CAN do, not on what I can't control.
I also agree that it's wrong for anyone to ruin someone else. But when that happened to me, there was nothing I could do except continue to live my life and prove them wrong. It took several years, but I came out better than before when the person was spreading lies about me. There were times when I was angry, but I never once thought about revenge because I know what that can do to a person.