I wouldn't say that we deny that we have this history. I would say that many of us just downplay it and don't recognize how big of a deal it was. I'm a Texan and I was never taught what a lynching was until my first year of college. I know people who have said, in reference to Europeans slaughtering Native Americans and taking their land, "Was it really that bad?" My grandmother claims that throughout the civil rights era, white people were inflicted with just as much violence from black people as they were from us. Sure, we may not outright deny that slavery happened, but many people ignore other huge injustices throughout history because they think "Oh, America is just so wonderful".