But for higher-ranking officers, I can't help but see Iwo Jima as a huge failure and black eye for them. I'll admit I'm no big-time expert so someone will correct me if I'm wrong. But there were ways that these heavily-defended islands could have been bypassed.
Iwo Jima was a stragegically valuable island.
Iwo Jima was of necessity to our plans. The U.S. held no islands in the Pacific for our planes to land, refuel or repair for bombing raids on Japan. Plus, once the islands were taken, it was a foregone conclusion that we would be invading Japan. We wouldn't have been able to do it unless we had possessions of these islands as a stepping-stone. Granted, the A-bomb eliminated our need for these refueling stations, but at the time of these island battles, no one knew that the A-bomb would be used to help end the war.
Some heavily-defended islands were bypassed.
Iwo, however, was taken because we needed Iwo Jima as an emergency airfield for B-29's that were damaged over the Empire and couldn't make it back to Saipan and Tinian.
Roughly 2000 B-29's (carrying 20,000 crewmen) landed at Iwo.
As noted in other posts, there were some islands that were bypassed. Three that immediately come to mind are Truk, Rabaul, and Formosa (Taiwan). They could be neutralized by air attack and isolated by sea blockade, which was a heck of a lot easier on men and material than taking them by storm.
IIRC, in the 1980s resurgence of interest in NBC (now CBR) warfare and defense, there was an article in the Marine Corps Gazette on the theoretical use of chemical weapons (nerve gas as I recall) to take Tarawa. The author argued (based on weapon effects and casualty tables) that a chemical attack would have produced fewer casualties for attacker and defender than the actual battle did.
Unfortunately (and fortunately) almost all the senior Marine and Army officers making the decisions about the use of such weapons had WWI Western Front experience with chemical warfare and had no desire to repeat it. The same can be said about senior officers in Great Britain, France, Germany, Italy, Russia, etc. So the chemical weapons stayed in storage and we did it the hard way, not only in the Pacific but also in North Africa, in Western Europe, and in Russia. As is frequently commented by historians, it says a lot about how horrible the experience must have been if even a fanatic like Hitler would rather see Germany defeated than resort to use of chemical weapons. (Of which, Germany had plenty.)
(In fairness, I should note in passing that the main land force opposing Germany for most of the war, the Soviet Union, had suffered tremendous chemical warfare casualties (as Imperial Russia) at the hands of the Germans and Austrians in WWI. It consequently devoted a lot of time and effort to built up a chemical offense and defense capability during the latter part of the interwar period. The Soviet Army had some hundreds of thousands of well equipped and trained soldiers ready to defend against chemical attack and to conduct chemical attacks. So any temptation German planners may have had to use such weapopns was also probably tempered by the realization that the Soviets were far better prepared to play offense and defense than the Wehrmacht was.)
I preface my reason for making this statement:"History is inviolate" so is anything to be gained by being overly critical of past seemingly bad decisions and then doesn't hind sight become an exercise in futility as it revisits many sad, sad memories, unnecessarily, concerning the terrible losses incurred especially by those who lost loved ones as a result of these "decisions".
As far as we will ever know these wonderful human beings died willingly in the place of others who would benefit by their selfless sacrifice and in their stead and for them we must believe it was the right decision by their leaders or else the discussion becomes an argument with the winner being "the one who could holler the loudest"
Again, "History is indeed inviolate"!