An interesting parallel thought experiment: "What if Roosevelt Decided to Use the A-Bomb on Berlin?", which has been covered a few other places:

1) Some of the same justifications existed as Nagasaki/Hiroshima bombings. Ending the war earlier with fewer Allied casualties, controlling Berlin before the Soviets arrived, etc. In hindsight, many death camp lives may also have been saved.

2) The Soviets took 300,000 casualties taking Berlin in April '45. Taking Berlin in March (as some had envisioned with the "Patton turned loose" theory) would've been even bloodier.

3) The original impetus for building the A-Bomb was beating Hitler's Heisenberg to the punch. Once Germany fell, many Manhattan Project physicists (who were from Europe, some Jewish or like Fermi married to Jews) signed a petition to not use the bomb, anywhere.

4) A moot point, I suppose, as the A-Bomb was not quite ready at that point.

5) WW II was a rather unique situation, perhaps nothing since has reached that level of A-Bomb justification, thank goodness.