I'd like to mention a couple points:

The IG Farben Buna at Auschwitz-Monowitz was bombed, though. It was only 3 km from Auschwitz-Birkenau.

The morale of the prissoners was crashed, after they saw hundreds of bombers pass by.

Bombing the railroads, the krematoria or the gas chambers could have stopped operating for days, maybe even weeks. And let's not be light about this: in March 1944, when the deportation of Hungarian Jews was at its height, 12.000 people were being killed everyday. No railroads for 10 days: 120.000 lives.

I do understand the Allies' strategy: destroy the German war machine and the Holocaust would stop. Yes, but I think it's precise to notice that 1.300.000 people were killed at Auschwitz, many, many more than the British, Commonwealth and American total war casualties combined. Also, anti-semitism can be traced to several episodes involving the Allies in those times. Light antisemitism or indiference, maybe, but it cost lives as well. What about the liner St. Louis, by example?