I learned from high school history textbooks that wiping out Hiroshima and Nagasaki was justified because invading Japan would probably have meant the deaths of 10s of thousands of U.S. soldiers.
Apparently, the moral calculus of trading those lives for hundreds of thousands of civilian Japanese lives didn't need to be discussed, because it wasn't discussed.
It wasn't even possible to discuss, really, not in Iowa where I went to school. Anyone suggesting that it was morally wrong to destroy those cities and kill all those people would face hostile accusations of not "loving" the U.S. and not caring about our soldiers. The reality of hundreds of thousands of Japanese dying, many of them in agony, was almost universally considered acceptable, because they are not us. They are Other.
Not much has changed in how we think, Even though more Americans recognize now that nuking Japanese cities was not a military necessity.
We still value patriotism, which is almost by definition Othering. We still pick sides in conflicts and cheer for slaughter. We still believe killing civilians is just fine so long as we use big words like "collateral damage" to euphemize the slaughter.
My former business partner almost became collateral damage in Iraq in the first Gulf War. He was 12 years old, running through the night with his little sister and mother, holding their hands and screaming as bombs rained down on his town.
Most of his immediate family burned to death that night, but their deaths were "morally justified" according to doctrines of collateral damage.
This is who we are right now, and who we are is a very ugly picture.