The single greatest night of destruction in Japan during the war was not either of the nukes but the fire bombing of Tokyo. If the Americans didn’t make the nukes, at some point someone else would have. That’s the beauty (and interesting thing) about technology - it’s inevitable. You really can’t pick and choose. You can slow it down sure but never fully stop it.
If you want to understand the world and this topic with more nuance than a teenage hippy sayin “nukes bad Mann” then I will recommend “The making of the atomic bomb” by Richard Rhodes.