My late writing partner once described to me the dangers of revisionist history as a blight on the collective memory of the world.
The fact that there are people who against all reason and evidence claim the holocaust never happed place themselves in the historical cannon, and as the events move in to evermore distant history, out of living memory then all that remain are the testimonies of the witnesses and historians among who will be the deniers seeding doubt for the remainder of time.
For every thousand historians who tell th truth, there is and always will be one who says it was all a lie, diluting the facts.
We all know Princess Diana died in he tunnel in Paris in 1997, but there are those who claim it was faked, she lived on elsewhere, in 100 years time reports from 1997 and 2017 won't seem that far apart, and some of those guys made a pretty good case and of course there is no proof she did not fake it.... etc, etc etc.
Fake doubt is the cancer of history, and it must be a great comfort to the modern Fascist to think he is being unjustly blamed for a holocaust that never happened in the war years, propagate by people who just have it in for his ideology and want to silence his "truth".