I am always ashamed of FR discussion on the atomic bomb (or even conventional bomb) incineration of cities as such: not, strictly speaking, collateral deaths, but when city = target.
The indiscriminate killing of civilians in war is a crime similar to the killing by massive abortion (50,000,000 victims since Roe vs Wade) in this respect: that we dare to offend Almighty God by the deliberate shedding of innocent blood, which He calls an abomination.
The trouble is in war, innocent blood will be shed. The bombing of cities was not a good tactic (other than being immoral). For instance, in Germany it was thought that bombing and killing the factory workers would slow production. It didn't. Dresden and Hiroshima are part of the reasons that we don't do carpet bombing of cities anymore.
But in 1945 the Allied command had two or three choices. First was ground invasion, which would have devastated Japan and realistically cost a million lives (probably more). Second was a blockade. Which had already failed to incapacitate Japan, and would have had to starve a good portion of the population to death before they surrendered. The third was the atomic bomb.
No good choices there. No way to not kill innocents, no way to just go home and say "Game over, you guys lost." War is like that. If we pulled back and just said "Oh well", Japan would have rebuilt and attacked.
The choices for targets always confused me, and I do not agree with them, but to be honest I can't think of a way that would have got Japan to surrender cheaply.