Interestingly, conservatives at the time were in the forefront of condemning Truman's decision to drop the bomb.
Which Republicans decried the use of the bomb?
The death of Japanese civilians was to be horrific had we invaded. Millions dead from battle, tens of millions from disease and starvation. We were able to end the war by killing 400,000, a much smaller number. It was a good humanitarian decision.
WWII was a war that did involve the killing of millions of civilians, but that was started by the other side with the V1s and V2s that hit London. It was continued with the bombing of Coventry by the Germans. I do not accept that the Coventry bombing was a mistake as accurate air navigation was long established and it is simply unlikely. Really unlikely.
In all cases, the other side began the reign of civilian terror, Japan in Korea and especially China, Germany in England and Russia.
Our primay requirement was to destroy manufacturing capacity and most all of our bombing was designed to do so. But bomb drops were exceedingly inaccurate by today's standards, the Sperry Bombsight adding a lot of accuracy but not enough to keep the collateral damage to a level that is consistent with today's standards.
And I think you should read some more on WWII. Your knowledge of that conflict is not up to snuff. I know that because you have no real realization of the difficult position that we were in nor do you know what the concept of Total War means.