Its not pardonable, but it is understandable.
People genuinely have trouble understanding just how different the world was back then. My grandmother (who lived in eastern Europe for her whole life) first saw a black person in person when she was in her 70s in the late 90s. She was more shocked than anything else at how dark his skin was.
She grew up in an extremely white country. The first set of slightly darker immigrants, the gypsys, set a very bad example of different people were like. They were probably just trying to survive, but to the natives of that country, the gypsys were vulgar and violent criminals.
Now imagine you are in an African or middle eastern country. What would your opinion of the US be if their first ambassadors were members of the KKK. You would think that the Americans are terrible racists. While the analogy doesn't hold up for many reasons, the effect is the same. Bad first impressions and bad experiences lead to a way of thinking that is logical but incorrect.
So while I cringe at the stuff I've heard throughout my life, I understand that not everyone's life is the same and that I haven't had to experience what they have.