This is an excerpt from "Always/Never" from Sandia.[1]

[1] https://newsreleases.sandia.gov/always_never/

Sometimes I wonder if things would have turned out better if the Manhattan project scientists had done their calculations about if the nuke would set fire to the atmosphere and discovered that it in fact would. At that point, you wouldn't do any nuclear weapons testing unless you wanted to run the risk of killing all humans, and I wonder if that would have completely stopped nuclear weapons development, as you could never test if they actually worked without significant risk.

I know that there are discussions about how the war in Japan would have ended if the US hadn't dropped the nukes on them, I've heard that it would save a lot of lives, and also that it would end a lot of lives, so I don't really feel like I know enough to weigh in on that discussion :/