I find it atrocious, and possibly should have been avoided, but it's easy and convenient for us to sit in front of our laptops and pass judgement 70 years after the fact, without having first-hand experience of the situation at the time.
Personally, I think that any nation involved in the war, if they had been in the same position of the US, would have taken the same decision, but again it's easy to judge and theorize now.
Do you think that it's acceptable or "rational" as you put it to have people fried alive in furnaces or dissolved in acid?
Would you like to face a similar "rational" fate for you or your loved ones?
Hadn't been for the US and its allies emerged as victors in WWII, all of their political and military leadership would have been had their own Nuremberg trials a decades ago but they got it away with it for the simple fact that they prevailed over their enemies.
Like they say 'History is written by the victors'.
I, for one, am glad that the Allies won the war. The lesser of two evils.
Or we could light their cities on fire with bat bombs. War is hell.