Isn't "war crime" a stupid concept?

I'm not saying killing civilians, raping, pillaging, and concentration camps are alright. However, lining men up and telling them to shoot at each other, against their will if they're drafted, doesn't seem like less of a crime to me. Furthermore, making a quick and decisive victory by any means necessary and ending the conflict as soon as possible seems like more of a mercy than letting a war drag on. However, one would think war its self is the actual crime, making "war crime" redundant.