It's an interesting subject, and its very hard to approach. (Take this as a fantasy world topic). I've always been very pro-good/neutral supporter. Meaning I support the forces of good that include humans, elves, dwarfs, etc. And have a distaste for the forces always viewed as dark. Orcs, Goblins, demons and so forth.Though I have been known to side with the dark when necessary to further my goals.
Now here's the question. If you had the chance to end the war for good and ensure the survival and stability of your own kind, would you eliminate and commit genocide against your enemy? Regardless of the start of the war. Be it for land, food, simply because of centuries of hatred. (A good example is the game Ninety-Nine Nights. When playing as humans, you have a chance to not only attack the goblins homeland, but kill women, children and the old in retaliation for a similar attack against humans).
The idea of killing innocents has always been a touch and go subject in our society, but if it comes down too it, one has to choose. Them or yourselves. Put yourselves in the shoes of such actions. Your family is huddled back in your small town, your sword in hand and another wave of marauding Orcs are heading your way. The knowledge if you die, your family does as well. Battle after battle, constantly keeping them at bay. Now if information happened to come your way of where these orcs lived...would you not wish to go there and destroy them? To protect your family? Your children? Loved ones?
Keep in mind that these orcs and goblins are not the mindless, slobbering races that they are always cut out to be. They have familes and culture themslves...and the fact that peace between such will more then likely never come to be.
If you don't want to look at it in a fantasy type fashion, then take it as a real world situation. War is a constant here. Its part of our nature even if you don't believe it. There will always be conflict over food, water, religion and just for different political views. Both sides want to win, and war can drag on for years. So if you could end it, by destroying all of them, to save your own...would you?
The threat of constant war? Or peace through destruction? What would you do?