The twelve men who flew on the world's first nuclear bombing mission in 1945 made history, as they deployed "Little Boy" over the city of Hiroshima, Japan. The youngest was only twenty at the time. For the rest of their lives (only two still survive) they were asked about their motivation and whether they thought it was worth it. Mental_floss has quotes from almost all of them, and a discussion in the comments from those of us who can only see the event in hindsight. Link
Debating and bickering about how it prevented millions of lives vs. it was not necessary, in 5, 4, 3....