Imagine being one of the Allied soldiers who stumbled upon Auschwitz and the other death camps in the last days of the war. Imagine seeing the horrors, this firsthand evidence of the cruelty man can inflict upon his fellow man. It shook many brave men, who had braved Normandy, the Bulge, but nothing could prepare them for this. Both Eisenhower and Patton vomited at the sight; Patton was tempted to order all the guards executed en masse for these atrocities.
Now imagine you're on the other side of the fences.
Nazis. Most of the German people had no idea this was going on until it was uncovered. Well, they knew that the Jews were being rounded up, along with anyone else who was "different", but they didn't realize it was this bad.