I see this “mindset” in the following way - there are times when ordinary morality can be superseded by the needs of a greater good, or higher cause (ie war, basically).
But this philosophy cannot be unchecked (or else you wind up with Aushwitz and the Killing Fields). Hence we have the Laws of War and Crimes Against Humanity that limit (under threat of punishment) the degree to, and circumstances under which, the “ordinary morality” can be superseded during wartime.
Unfortunately it has often gone unchecked and at times to grotesque levels. The victims of stone cold common criminals, the minions of Lenin, Stalin, Hitler, Mao, Pol Pot, the Rwanda genocides, Turkey’s massacre of Armenians, the summary executions of entire populations recorded throughout ancient and recent history.
Give Woody Allen credit. He summarized it best and had great psychological insight. When accused of being an agnostic Jew and indifferent to the Holocaust , his answer was priceless. “ I have no doubt that 6 million Jews were murdered, but my fear is that records are made to be broken”. Lets not forget that Mao in the 1950’s broke that record overtly killing by some estimates 60 million Chinese. It must also be remembered that he personally did little or none of the killing but had no trouble finding goons, thugs and henchmen who avidly did the murders. The other despots also had no trouble recruiting mass killers. People should always realize that such people continue to exist among us and the thin veneer of law, civility and religion has not proven to be impenetrable barriers to their vile actions given the right political circumstances. Americans are not immune to this behavior.