Revenge has two faces,  the good and bad revenge.  
I believe that revenge can sometimes be a learning also to those who hurted you.  

They may not know that they hurted someone unless it bounce back to them.
  
If it's result positive thing to someone you've revenged  and to you also then it is good.  But if it's hurted you more and got to the point that you destroy even your self,  then it is bad.