We can't be surprised a sizable portion of society doesn't believe it happened. First it's horrific which by itself makes it difficult to comprehend. In that regard it's no different than the huge death toll from Communism in the 20th century, just too massive to comprehend. Second, we're now 80 years away from the end of the war and almost everyone who lived it has passed. We have almost nobody left with first hand knowledge of what happened.
Last summer we toured Normandy and our guide said he was worried about history repeating itself because there was nobody left to pass on the knowledge first hand. He recalled hearing from his grandparents about the Nazi occupation and the eventual liberation by the Americans and Brits but said they were gone before they could teach his kids. It's significantly different reading it in a book than it is hearing it first hand from people you know and love and trust.
As to this specific survey it's no surprise Democrats are twice as likely not to believe as are Republicans. It takes a high level of naivety to be a liberal and with that comes an inability to accept that humans are capable of doing some really awful things. It's a huge part of what makes them dangerous. History repeats itself because naive people refuse to accept that it ever happened in the first place.
The federal government was never meant to be this powerful.
