We often think of seeing the one who did you had suffer. Mostly what goes around Comes Around and you get to see them pay for their vices but the moment you feel happy about it, what you feel is no longer happiness.
The happiness is that feeling which comes out of fulfillment and positive thoughts. What you feel when you see another soul suffer or pay for their mistakes is a cruel selfishness.
The moment you realise it you stop feeling happy. And thus you grow as a person. So stop feeling happy when people pay for their mistakes. Grow above petty pay backs.