I think we have a right to seek revenge against those that wage war against us. That is the difference. We are justified they are not.
We don't "seek revenge." We seek to punish those who murder or aid murderers.
If we were into "revenge," we would just bomb Arab towns or kidnap the wives or children of al-Qaeda members and kill them.
"Revenge" is what "they" are into. We are better than they are.