To begin with the Japanese mainland was not combative territory. They were civilian manufacturing centers (part of the War effort yes, but civilian areas nonetheless.).
Secondly, The tactical nature of that incident, and the torture of ILLEGAL COMBATATANTS is the same. To gain an Immediate advance in the saving of innocent lives on our side of the equation.
And from a Moral Standpoint, you cannot coherently compare the intentional infliction of severe physical discomfort of one illegal combatant atr a time, to he mass infliction of slow sure tortorous death to civilians.
Truman, to his credit said he never lost a minutes sleep.
That's because he did the Right thing. As are those that go to the necessary legnths to extract the information that keeps innocents alive.