The taboo issue also looms large. I think any intelligent person should find the evidence for the Holocaust compelling. At the same time, I find it somewhat disturbing that we've reached a point in Western history where agreement with a particular interpretation of a historical event is seen a non-negotiable part of being a morally 'good' person. That this is an absurd way to think ought to be obvious, but it apparently isn't to most people.
Dr. Novick touched briefly on another issue that doesn't receive nearly as much attention as it ought to, namely the way the Holocaust narrative is used on contemporary discourse. For Jews, it has become a discourse of exoneration, a get out of jail free card that has allowed, for instance, the Israeli government to act with near impunity against its neighbors (and against Arabs living within Israeli occupied territory). For others, it is a discourse of guilt, a silly 'never again' rhetoric that drives policy decisions that are objectively against the interests of the nations that pursue them (see Iraqi Freedom, Operation). And still for others (present enemies of Israel, primarily), it is a narrative of cynically manipulated fear (see Iran). None of these narratives are productive or helpful, and their continued use to bludgeon the political opponents of the unfettered domination of Israel over its neighbors in fact is a major driving force behind revisionism and Holocaust denial.
I think there's a degree to which the way the Holocaust is decontextualized in Western (and especially American) education that also breeds resentment. Because the Holocaust is taught as a seperate event, its connections to the wider historical context of its time is lost. The Holocaust is unthinkable without the military conditions that prevailed in the early 1940s, yet it is rarely taught in the context of the war. Worse, it is taught as a specially heinous crime targeting a special people, which not surprisingly, breeds resentment (the more so given that essentially half of Hitler's victims weren't Jews at all, and despite occasional genuflections in the direction of Gypsies and homosexuals, the Holocaust is still taught almost exclusively in the context of Jewish suffering).
This tendency to teach the Holocaust as a special event with no historical parallels obscures the fact that it was one of many genocides in an age of genocides. The Holocaust wasn't a unique event that could only have happened in Germany to Jews, and only at the direction of Adolf Hitler. Rather, it was an archetypal example of an evil built into the fabric of the modern nation-state: systemized, centralized and industrialized violence as a political tool. It's a pattern that began with the Conquistadors and the trans-Atlantic slave trade, was instutionalized by the Terror, intensified and industrialized during the 19th century colonial expansion, made the chief instrument of state policy by Lenin, Stalin, Hitler and Mao and made endemic to much of the world through the post-colonial adoption of Western organizational models. The Holocaust is just one of many such events, but that gets lost in the sociopolitical shuffle.