Understood about a port being a target, but that job good have been done with conventional weaponry via air. We to this day have been the only country to use nukes. How long do you think that will last...and can we get mad when someone uses, what we used against us ??? Rules of engagement are establish by what you do. Anyone who thinks that we would have not won that war without having to drop TWO nukes (that killed mostly civilians) has no idea how successful are conventional bombing was using B-19 and firebombing. We dropped the nukes simply as a form of show..Now the question remains. Do you reap what you sow ???
Consider this. In a war, a nation's core duty is to protect the lives of its citizens, and to hell with the others. That's a hard truth, and I see no wisdom in sugarcoating it.
A series of conventional strikes may or may not have ended the war before the invasion of the Home Islands was to begin.
And a series of conventional strikes would have required thousands of bomber sorties, with attrition (US servicemen dying) from both Japanese defense efforts and the immature design (in-flight failures) of the B-29.
The nuke had two salient advantages: one bomber per mission, and the shock effect (psychological, not just physical) of this plainly awful new weapon. Demoralizing the enemy is an effective, efficient way to prosecute total war, and make no mistake: we were at total war with Imperial Japan. This wasn't only show, but a way to compel an outcome in a timely manner that might not have been compelled with a much deadlier, more protracted conventional (incendiary) campaign.
Imo that puts paid to the moral question.
As for the setting of the precedent, look how long we've gone without another nuke being used in anger. In fact, a historian has made a strong case for the unlikelihood of an actual nuclear war in our foreseeable future. (The book to read is
Twilight of the Bombs by Richard Rhodes.) Our biggest threats of a nuclear bomb being used on a living target comes these days from terrorists (so far, so good) or from a "rogue state" in the somewhat unsavory modern parlance. But with the five "traditional" nuclear powers retaining a pretty good capability, a bombing by one of the newcomers (Pakistan, israel, perhaps Iran) would lead to immediate and severe consequences ... probably not nuclear, but prosecuted with a ferocity the world hasn't seen from a first-rate power since the World War. No more pulling punches like in Iraq (twice), Afghanistan (first them; now us), Viet nam, Korea etc. The international community would be unanimous and total in its condemnation.
So I disagree on two issues, if I understood your post: that the use of the bombs was discretionary and left us with a moral debt ... or that we're under a nuclear gun of our own (indirect) device. cn