Well, I don't think there was anything special with the Germans in this regard. E.g. if you were somehow able to reproduce the same conditions starting from hundreds of years beforehand, ravenous propaganda the decades leading up to it, start off the genocide in the U.S. at the same timeframe, I'm not sure Americans would have fared any better. We weren't exactly nice to the Native Americans, for example.
But that wasn't really the question either. Of course the people should have known what was going on, especially by 1943. Even the example of "working the Jews to death" is horrific enough, and what did they really think was happening over on the Eastern Front?
Which was roughly 10 years too late. By 1934, Hitler had all the laws he needed to do whatever. Also consider that the Nazis are a example of hybris and self-destruction, I wouldn't expect anything to follow that pattern again, other than in the third world. Steady does it.
On the other hand, Dr. Bronner, the magic soap guy, emigrated 1929 to the US, changed his name from Heilbronner to Bronner, and urged his parents to follow him (you can find that on his wikipedia page). So at least when it came to Antisemitism, it was possible to sense it. But on the other hand, there were even Jews who fell for Hitler at first, and were sorely disappointed when their home country turned against them.
So while Hitler never fooled some, he did fool many enough for long enough. And compared today, those times were utterly low tech. Even the propaganda was just brutish. Which is why I like to use them as an example, they were still clearly recognizable for what they were; it got so much murkier after that. You could say it metastasized and got debugged.
But that wasn't really the question either. Of course the people should have known what was going on, especially by 1943. Even the example of "working the Jews to death" is horrific enough, and what did they really think was happening over on the Eastern Front?