Honestly, it's been a few decades and I don't recall many details (other than there being a lot of details). I don't remember if it was directly stated Nagasaki would have been destroyed with or without the A-bomb but I do recall reviewing a shocking analysis on the devastating results of fire-bombing Japanese cities and the escalating run-rate of civilian casualties as air superiority over Japan was established. I also remember seeing large estimates of U.S. troop and Japanese civilian casualties should the allies be forced to do a ground invasion city by city.
The allies had good reason to believe much of the Japanese population would fight block by block without a formal surrender by the Emperor and the Japanese ambassador had privately conveyed that the Japanese high-command would die in honor before surrendering in shame (which he sincerely believed). This was supported by the number of kamikaze pilots which seemed endless and continued to shock U.S. commanders.
> The allies had good reason to believe much of the Japanese population would fight in the streets without a formal surrender by the Emperor and the assessments were that the Japanese high-command would rather die in honor than surrender in shame.
That's not something that's ever been in contention, it's very much the reason that was put forward to justify the ongoing and (relative to A-bomb) cheaper conventional weapons HE-I bombing missions.
Hence my pointing toward that bombing program as the real root of inspection re: ethics.
The nuclear program (put into motion by the Allied MAUD committee) was intended for the German theatre and after consuming vast resources was left hanging when Germany surrendered prior to the Trinity device test .. the argument to test the two weapon designs was (at that time) very much a zero friction zero consideration kind of thing that dovetailed into the existing targeting lists.
Worth bearing in mind that either or both weapon devices may very easily have failed in the field.
My interest in that event lies with it being a prime example of something that just flowed into happening at the time and was later retconned into being some kind of deeply considered a priori known to be significant and pivotal event.