Millions did not suffer decades after unless you are referring to people who lost relatives. You have to look up the effects of radiation, our understanding has come quite far.
Also the blast was an airburst, which left minimal radiation after a period of time, vs a ground blast which would have left the area uninhabitable for a significantly longer period.
Background radiation in hiroshima and nagasaki today is indistinguishable from normal background radiation.
Are Nagasaki And Hiroshima Still Radioactive?
Why Can People Live in Hiroshima and Nagasaki Now, But Not Chernobyl?
Ionizing Radiation | Radiation Hormesis | Low Dose Radiation
Hiroshima and Nagasaki Cast Long Shadows Over Radiation Science - NYTimes.com
Nagasaki was bombed because the Japanese has not surrendered,
Japan refused the Potsdam declaration.
After the emperor broadcast his acceptance of terms, a military coup was attempted by sections of the military... does that sound like it was 'well established' that the imperial army was willing to surrender?
Maybe a section of the military was willing to surrender, but other sections weren't, and overall that lack of a coherent decision cost them.
Now this is just stupid. Lets ignore that an invasion of Japan would have led to drastically greater casualties for both sides...Why should American soldiers have less value to American leaders than Japanese workers? This was a battle of countries, all the country were combatants, as it was everywhere else the war was being fought. The firebombings and raids from all sides should make this self-evident. This wasn't unique to the US despite what you've been taught.