Is killing for vengeance in time of war justified?

When I look at the newspapers murders and slaying are potrayed in various amplitude. These news vary from murder used as a solution to settle petty disputes such as hassles in bar to mass genocide which happen under the pretext of preserving world security.

But, my question remains placid; is all this justified? Why we humans of all creatures, with such complex yet powerful brain, desire to perish our alikes. What really provokes us to permanently abolish our kith and kin. The more I ponder, I realize it is just materialistic attachment.

Never ever an eye for an eye is answer. I do not want to preach peace and proselytize humanity, which I feel our mahatma has done it enough. I feel majority of the world problems can be solved "&" - in background. Great warriors were not powerful, but very rational too. The true achievement to any feud, is to render the opponent weak through brains not by brawn. Craftiness and deception are good at times, if not always.