While i understand the rationale, ive come to question if "fighting fire with napalm" is such a good idea, from ethics perspective. Is it not a duty to not fall prey to indulge in mass killing even if it may seem justified by the barbarity of the opposing side?

It’s easy to question the decision when you’re not responsible for making it. When you’re not responsible for your soldiers’ lives it’s easy to talk about ethics. Invading Japan would have killed tens of thousands of US soldiers, easily. When it comes right down to it, you’ll always prefer the option that’s spares more of your countrymen than the enemy (who started the war against the US.) That’s perfectly ethical as far as I’m concerned - as ethical as anything can be in war.

That is true. I was not there and im of a completely different world. Well, to be honest i ended up agreeing atleast partly too. For context im from europe, and a small country arrayed against a historically and currently aggressive and strong neighbor, aaand i was conscript officer in charge of a few hundred men total. Believe me that im not that detached from this question, however my concience about bombing civilians is also quite conflicted but heavily leaning towards the Geneva Conventions.

In conclusion; no, i dont agree that it was be "perfectly ethical" or even simply ethical, but rather a neccesity born of the lack of efficacy in the firebombing campaing. And yes, a top-down hierarchical militant society like imperial japan of the time would not have surrendered without significant show of power, of imminent destruction, demonstrated. Im personally more convinced that Hirohito only issued the decree to surrender unconditionally due to the fear of imminent destruction of the capital, since a military society would always expect an attack on the command structure.

Allied casualties were expected to be in the high hundreds of thousands. (https://en.wikipedia.org/wiki/Operation_Downfall)

It is a duty to make mass murder stop in the most efficient way possible. The Japanese would not have surrendered for anything less than what happened to them, so this was proportionate and reasonable violence.

Nuking Nagasaki wouldn't do much to stop the holocaust. The Germans were already three months defeated at that point.