Not an easy question to answer.
The horrors we witnessed at Hiroshima and Nagasaki and the lessons we learned there have done much to change our perceptions but we have the benefit of hindsight -- a privilege denied to those who made the decision in 1945.
Yes, it was atrocious but the Japanese had themselves perpetrated many atrocities during WWII. Gladys Aylward, in her autobiography "The Small Woman" (later "The Inn of the Sixth Happiness" starring Ingrid Bergman) said that she could not believe the brutality of the Japanese in China when they had been such gentle folk before the invasion.
In 1945, the war had been dragging on for six long, weary years (almost 4 for America) and the world was tired. Most people linked to the Allied nations would have welcomed almost anything that would help them get back to some kind of normality -- and who could blame them?
So the bomb was dropped.
Of course, not everybody has learned the lesson and while the major nuclear powers understand the meaning of "deterrent" the rogue states do not, and could well precipitate a nuclear holocaust.
But of the major nations, not all politicians are in sync with the rest of the world. Two of the most infamous -- men who stated their willingness to use nuclear weapons -- were Senator Barry Goldwater and now ("If we have nuclear weapons, why can't we use them?") Donald Trump.
Cold War I has passed. Cold War II beckons. It almost makes Matthew 24:6 tenable.