This is about genocide. "Lt. DeBuin: Killing I expect, Mr. McIntosh, but torture? I can't accept that as readily as you seem to be able to. McIntosh: What bothers you, Lieutenant, you don't like to think of white men behaving like Indians. It kind of confuses the issue, don't it?" This is key: "The Civilized" elevate over "the savages"; but at the end, who is superior of whom? Masterpiece. Note: watch "Hombre".
Why are the Apaches so bad ? Why do the Apaches never speak ? Well, don't ask Burt because Burt doesn't speak either, but he knows. He knows everything better than the other idiots wandering around him. Especially than the young, unexperienced and naive Lt. DeBuin (who knows nothing).