This belief is mainly associated with racism, Anti-semitism and other elements of the extreme right. Holocaust deniers, who sometimes playfully refer to the Holocaust as the "Holohoax" put down the figure of 6 million dead Jews as being blown out of proportion by post war-time liberal propaganda.
Lies about the Holocaust
Some people, even in Germany blame Poland for the Shoah, on the basis that that death camps are now located in Poland's territory. Poland had no influence over it, because it was occupied, and the Holocaust was conducted by Nazi Germany. Blaming Poland causes severe diplomatic tensions.
The Holocaust and history
In reality the holocaust is one of the best attested historical facts and there was any amount of testimony from camp survivors, from soldiers who liberated the extermination camps, from the camps themselves and from photographs taken at the camps.
The holocaust was planned in advance and Hitler stated his evil plan.
Once I really am in power, my first and foremost task will be the annihilation of the Jews. As soon as I have the power to do so, I will have gallows built in rows - at the Marienplatz in Munich, for example - as many as traffic allows. Then the Jews will be hanged indiscriminately, and they will remain hanging until they stink; they will hang there as long as the principles of hygiene permit. As soon as they have been untied, the next batch will be strung up, and so on down the line, until the last Jew in Munich has been exterminated. Other cities will follow suit, precisely in this fashion, until all Germany has been completely cleansed of Jews. ( Adolf Hitler speaking in 1922)
Holocaust denial and the law
In many liberal and democratic countries Holocaust denial is a criminal offence because it is clearly based on falsehood and aims to malign the Jews who suffered so badly during the holocaust. This causes problems over free speech as we will never agree how far people should be free to say untrue things that do great harm. Slander and libel are not allowed even in the United States and holocaust deniers slander or libel whole communities of people who have already suffered, the Jews, the Gypsies and others.
In Britain holocaust denial isn’t illegal in itself but almost all the material the holocaust deniers use would be illegal in Britain because there incitement to racial hatred is a criminal offence. Despite this there was a British court case when holocaust denier, David Irving sued someone for libel and lost the case. Dr. Deborah Lipstadt wrote that David Irving was a holocaust denier and she was allowed to write that because that’s the truth. Here’s what the judge said,
Judge Gray found that Irving had "for his own ideological reasons persistently and deliberately misrepresented and manipulated historical evidence" in order to portray Hitler "in an unwarrantedly favourable light" particularly in his treatment of the Jews. Irving had "significantly" misrepresented, misconstrued, omitted, mistranslated, misread and applied double standards to the historical evidence in order to achieve his ideological presentation of history. Judge Gray also found that Irving was an "active Holocaust denier; that he is anti-semitic and racist, and that he associates with right-wing extremists who promote neo-Nazism." 
What holocaust deniers are like
Don't ask people you know to be Holocaust deniers where 6 million Jews went between 1933 and 1945, or else they will hit you with a big plank with a nail in it.
- Deceit & Misrepresentation, The Techniques of Holocaust Denial
- Criticism of Holocaust denial
- Holocaust denial
- Holocaust Denial on trial
- Holocaust Denial
- Photographs of Concentration camp victims and corpses
- List of Wikimedia photographs of the holocaust
- Holocaust Denial and the 2000 Libel Trial in the U.K.