Actually saved the lives of millions of civilians by preventing the invasion of Japan.
At the time, Hiroshima and Nagasaki were military cities, producing military hardware for the Japanese armies. They were military targets not civilian centers. Those two bombs could have killed a lot more civilians if we had targeted other cities.
The targets in Hiroshima and Nagasaki included military industries, which employed civilians, who were warned via dropped leaflets to flee the city. More deadly than Hiroshima, Nagasaki, Hamburg, or Dresden was the firebombing of Tokyo in March, 1945.
With the current nuclear war starting trajectory of the Biden administration, soon we will be saying: New York, Chicago, San Francisco killed mostly Demonrats, and it saved the world.