I've written on the Allies' alleged abandonment of the Jews during WWII. One serious issue confronting decision makers was how much credence to give growing reports of industrialized mass murder. Their reluctance to believe stemmed, in part, from a natural doubt that fellow Europeans could behave in such a barbaric manner, sure.

But I think the principal barrier to acceptance was memory of Anglo-French Great War propaganda, which accused the Germans of using the bodies of slain Allied soldiers to manufacture munitions, crucify Allied POWs, rape Belgian women & bayonet infants, destroy cultural landmarks & so on. I think a lot Americans in particular felt burned by it—fool me twice ... no thanks!

In his memoir, Crusade In Europe, Ike recounts that just after the German surrender he & his staff made it a priority to see the condition of concentration camps in the US sector. Bearing in mind the efficacy of atrocity legends from the first war they needed to see for themselves. And this from the Allied Supreme Commander.

When Wetzler & Vrba courageously escaped Auschwitz with accounts of mass murder how could their Allied interlocutors know they weren't planted by Polish intelligence? For what purpose? First, to goad a reluctant US into the European War; second, stress the urgency of opening a second front by cross-channel invasion (though these last two are speculation on my part).

In early '44 Oskar Schindler brought funds to the Jewish leadership of Budapest, along with a warning of dire happenings in the east. He was not believed. Not even by people tragically on the firing line themselves.