Bibi Netanyahu claimed that the Allies could have prevented the killing of 4 million Jews by air attack. This is fantasy.
Before the Allies were able to base bombing squadrons in Italy in 1943 it was not possible to fly the distance from Great Britain or North Africa to attack targets in Poland. The American B-17 bomber, with an operational radius of 1276km, had an operational radius too small to fly from bases in eastern England to Treblinka (1,460km), Majdanek (1525km), Bełżec (1600km), Sobibor (1,590km) or Auschwitz (1,327km). Auschwitz was just inside the operational radius of a B-24G flying from England, but far outside the radius of the requisite fighter escort. The Allied bombing raid on Auschwitz III in August of 1944 was flown from Foggia in Italy.
Bełzec, Sobibor, Treblinka and Majdanek had already done their awful work and been closed down by the time the Allies had taken Italy and were in bombing range of Poland. The Einsatzgruppe actions of the invasion of Russia were also complete. That is, there were 2 million killed in those camps (the Operation Reinhardt camps plus Majdanek) plus more in Chełmno. There were 2 million killed by Einsatzgruppen of whom 1.3 million were Jews. That is to say, the Nazis managed to kill 3.5 million Jews before the Allies were in bombing range of Poland.
There is argument that we the Allies should have attacked Auschwitz II in particular or its rail infrastructure (as we did attack Auschwitz III) since we attacked the rest of the Reich often regardless of the efficacy of the attacks. This argument might be sound, but it does not argue that any innocent lives would have been saved.
Bear in mind that Allied bombing was not precise. The Allies bombed large urban areas in part because that was where large numbers of industrial workers lived, but mostly because their factories were too hard to hit. So even if we were willing to task aircraft away from war-winning missions in 1944 (and we were willing to attack targets of secondary value by the end of 1944), we would not necessarily have hit what we were aiming at.
Netanyahu claims, however, that the attacks would have been efficacious. In this he is sorely misled. We know a great deal about air attack against German railways in the Second World War and we know of no cases where air attack caused German railway lines to be put out of commission for more than a few days.
If the Allies had had any idea of the throughput of Auschwitz (which we didn’t) during the war it might have seemed rational to bomb the camp itself, knowingly killing its inmates and staff alike. (Unlike bombing a German town where doctrine assumed that the inhabitants would take cover in hardened shelters, it could be assumed that Auschwitz did not have shelter capacity for its inmates.) Without knowing the throughput of Auschwitz-Birkenau, however, that would not have appeared a legitimate way to put the camp temporarily out of commission.
Also, from what we know of attacking other German industrial facilities, including Auschwitz III, the facility would have been only temporarily put out of commission. Even the most intense Allied bombing raids conducted with heavy bombers based in Great Britain (Auschwitz would have had to be bombed by light bombers from Italy) rarely caused lasting damage to German industrial output. Consider, for example, the massive Allied raid against German ball-bearing factories in Schewinfurt which managed to disrupt production for only a few weeks.
If Auschwitz-Birkenau had been put out of commission for a period of, say, a week in 1944 it would have delayed the destruction of any number of Jews until later in 1944. Bear in mind, however, that when the Red Army entered Auschwitz in 1945 it had already done its work. The few prisoners who had survived to be death-marched away from Auschwitz were alive because they had been selected for death by forced labour, not because the Nazis had been interrupted in gassing them.
Make no mistake, the best result that could have been achieved would have been the temporary slowing of the process of extermination for a matter of days, in return for the deaths of many in the camp (had it been attacked directly) or many in railway trucks (had the railway lines been cut for a few days).
As with so many things in war, to stop Auschwitz required putting Soviet soldiers on the ground with bayonets to chase the SS away. Stopping the Nazis required putting Soviet soldiers in Hitler’s garden. Effective, low-risk speedy air attack was not an option.
There is an argument that we should have bombed Auschwitz II or its railway infrastructure regardless of the inefficacy of that process, and regardless of the inevitable losses of bombers in the process. We must not, however, deceive ourselves into believing that we could have stopped Auschwitz or saved 4 million people in the process.
The point is, if you want to stop genocide you have to act much, much sooner.