Prof. Daniel Gilbert has written a delightful piece on the human tendency to take revenge set against the background of the current Middle-East conflict. It includes results of some psychological studies of conflicts which are pretty interesting. Intuitively, we knew that Gandhi was right and now some scientific evidences are coming.
I do not believe that responding to an injury caused by some one is wrong and am not a total pacifist. But I do believe that responding to every attack is wrong because it is dumb. Sometimes, not responding to attacks can lead to a bigger future gain. But that calls for an ability to give up short-term gratification and also (incase of countries) strong statesman who are not led by public opinion if that opinion is wrong.