So, the psychology research disagrees. While there IS a cultural/social component, there does seem to be a difference in people's disposition.
The big evidence there can be change is the Milgram experiment, where people who had first hand experience with the Holocaust immediately saw what was going on and refused to take part. That was an aberration, though. People aren't being forced to confront things on that scale in that way anymore, and even then it didn't work on everyone.