Well, the first holocaust revisionist had been in the camps himself:
en.wikipedia.org/wiki/Paul_Rassinier
Paul Rassinier (1906 – 1967) was a French pacifist, political activist, and author who is viewed as the father of Holocaust denial.[1] He was also an anti-Nazi French Resistance fighter, and a prisoner of the German concentration camps at Buchenwald and Mittelbau-Dora.
1949–1967: The author
By 1948, Paul Rassinier had been a history teacher for over twenty-two years, and was distressed to read stories about the concentration camps and deportations that he claimed were not true. He was also appalled at the unilateral condemnation of Nazi Germany for crimes against humanity that from his experience in Morocco, he did not consider unique, and claimed to fear that nationalistic hatreds and bitterness would divide Europe. As he explained it in The Lie of Ulysses:
one day I realized that a false picture of the German camps had been created and that the problem of the concentration camps was a universal one, not just one that could be disposed of by placing it on the doorstep of the National Socialists. The deportees—many of whom were Communists—had been largely responsible for leading international political thinking to such an erroneous conclusion. I suddenly felt that by remaining silent I was an accomplice to a dangerous influence.
Rassinier's first book, Crossing the Line (1949), an account of his experience in Buchenwald, was an immediate critical and commercial success, one reviewer describing it as "the first testimony coldly and calmly written against the demands of resentment, idiotic hatred or chauvinism".[18] The Trade Union of Journalists and Writers also praised it, and it was recommended reading by the SFIO.[19] It is notable for its criticism of the prisoner government. Rassinier claims that effective resistance was found only among the Russian prisoners, and that many brutalities in the camp were committed not by the S.S., but by the mainly Communist prisoners who took over the Haftlingsfuhrung and ran the internal affairs of the camps for their own benefit. Rassinier blamed the high death rate at the two camps he saw on their corruption.
His second book, The Lie of Ulysses: A Glance at the Literature of Concentration Camp Inmates (1950) caused controversy. Rassinier examined what he considered to be representative accounts of the camps. He criticized exaggerations and denounced authors, such as Eugen Kogon, who in L'Enfer Organisé (1947) claimed that the Buchenwald prisoner government's main objective was "to keep a nucleus of prisoners against the S.S." Rassinier asserts that this nucleus of prisoners were only looking out for themselves, and further claims that the Communists were trying to save their own skins after the war, saying that: "by taking by storm the bar of the witnesses and with extreme shouting, they avoided the dock". He also describes his visits to Dachau and Mauthausen, noting that in both places, he got contradictory stories on how the gas chambers were supposed to have worked, and for the first time expresses his doubts on the existence of gas chambers and a Nazi policy of extermination.
The book created a scandal, and on 2 November 1950 was even attacked on the floor of the French National Assembly.[20] More because of the foreword by Albert Paraz than for the content of the book, both Rassinier and Paraz were sued for slander by various organizations. After a see-saw round of trials and appeals, both Rassinier and Paraz were acquitted, and an expanded edition of The Lie of Ulysses was published in 1955, which sold well. However, the uproar led to complaints from members of the SFIO, and on 9 April 1951, Rassinier was expelled from the party "in spite of the respect which his person imposes", as the expulsion document noted. A rehabilitation effort by Marceau Pivert was rejected.