So, World War II. We won the war and didn’t have to kill every last German or Japanese or Italian.
“If someone disagrees with you, threaten to kill him. If he still disagrees, actually kill him. Now there is no disagreement. Is logic.”
Except what if you’re wrong and he was right? That’s not logical, to kill the guy who had the right answer just because you illogically didn’t accept that you were wrong.
Of course in real life, even in a war, there are ways of resolving arguments that don’t involve killing people who don’t agree with you. Even in wars, battles are fought until one side runs away or surrenders, because running away or surrendering is more logical that fighting to the death after your side has already lost. And it is logical, if you are on the winning side, to accept the surrender of the losing side, because otherwise you’ll have to fight them to the death and more of your side will get killed even though you’ve already won the battle.
And this is where the panoply of “rules of war” developed, because wars aren’t about murdering each and every person you disagree with. Wars are fought over other issues–who gets to be king, where the border of our countries are going to be, how much tribute one side pays to the other. The people on the other side might be trying to kill you today, and might be fighting on your side tomorrow against a third party, or providing you with valuable goods and services. Or maybe you’ll be the one paying tribute, but still alive. You take his guys prisoner, he takes your guys prisoner, is it rational to kill them all or more rational to exchange them?
Or to take a modern example, the United States just had a war against Iraq, maybe you heard about it on the news. Should our strategy have been to exterminate each and every person in Iraq? I thought the point was to free them from the dictator Saddam? Or is the point to kill Saddam? Is he the enemy, or is his army the enemy, or is Iraq as a whole the enemy? What’s the point of the war?
War is just an attempt to use force to make the other guy do what you want him to do. The point isn’t to kill him, if he only would agree to do what you want you wouldn’t have to kill him.
The parts about war that you think are irrational only seem irrational to you because you don’t understand why human beings fight in the first place, and what they hope to accomplish by fighting.