I have seen the most amazing arguments over this subject, and I doubt this will put the matter to rest either. Given the way we carpet bombed German cities, I do think it's a good question., however I can also think of many possible answers that might have seemed sound at the time.

It's interesting to compare this with the arguments about whether we ought or ought not have nuked Japan, which entails the opposite sort of complaint.

bombed because it would pull resources from the overall effort of winning the war and putting a stop to all of it. I think Gilbert argued that the 450,000 Hungarian Jews shipped to death camps might have been spared had the allies bombed the rail lines.

It's all hazy (read this book when it first came out) and I could certainly be wrong.

Depending on the location: If in enemy territory let them go free and cause overuse of food supplies. If within German territory I would think they would had either left them in the rail cars or taken them out to a location nearby and and shoot them. Isn't that what they did with some of them under other circumstances? Failing that they would have utilize other methods.

The Nazi's didn't have scruples about what they did.

With the benefit of many decades of hindsight. During the war, people made decisions based on the exigencies and priorities of the time. Nowadays, it has sunk in what an awful crime the holocaust was, to the point where it is certainly one of the most well-known and lamented aspects of the entire war, which is saying something given the totality of the event and the enormous number of victims and the amount of destruction and suffering.

In 1944, what was known about the holocaust was subsumed into a much different matrix of conceptions and priorities. For military planners in the US, the priority was winning the war, as it always is in wars. If you and I went back in time, maybe we would argue that resources should be diverted to mitigating the impact of the genocide. But at the time, I imagine the thinking was that the best thing for the Jews would be to win the war as soon as possible. Every plane that was diverted to strikes in Poland and Hungary was a plane that wasn't bombing a rail line, factory, or military target in the West. The priority was to defeat Germany military and resources were directed to achieving that outcome as quickly as possible. I'll bet the argument against using military power against the Holocaust was that it would be a wash, since such diversions would lengthen the war and increase the amount of time the Nazis could commit mass murder, even as it might impact their ease of carrying it out.

This isn't an uncommon way of seeing things. Frequently state and social actors have many smaller goals under an umbrella of an over-arching larger goal. The larger goal (in this case winning the war) often takes exclusive priority. Early Bolshevik feminists in the Soviet Union were on board with giving women more rights, but they often had harsh words for Western 'bourgeois feminism,' even though on the surface they would seem to have something in common. But the Bolsheviks argued that energy spent on women's issues was better spent achieving the class revolution, which had to happen in order for the stage to be set for real women's rights advances. Kind of the same logic here. Win the war and you remove the threat to the Jews for good. Divert resources to mitigate the holocaust and you're doing some good, but you're lengthening the time the Jews are vulnerable to the Germans, even if you manage to blunt the killing, they can still do it. Best to achieve the main goal as quick as possible, since it's achievement is also the achievement of all of the lesser goals.

He could well have hit the prisoners and spared the Nazis.

Then, the only issue post-war would be who killed one's ancestors, friend or foe?

I hesitate to second guess in that instance.