The Holocaust is arguably the single best researched event in Western history. Hundreds, maybe thousands of historians have devoted large portions of their lives to understanding what happened, how it happened, and why. There are also countless memoirs devoted to the subject (more on this below).  No single person could possibly read all the books and articles on the subject - that's what annotated bibliographies, syntheses, and footnotes are for.

The research has amassed a body of incontrovertible facts, as well as other assertions that are subject to more or less debate. Examples of the established facts are that by the end of 1941 the German leadership had decided on the complete extermination of Jews in those parts of Europe under its control; that this decision was carried out with a ruthless efficiency leading to the murder of the overwhelming majority of Jews living in German occupied lands - roughly five to seven million in total; that the Germans steadily refined their technology of annihilation from mass shootings to an assembly line of death culminating in the gas chambers and crematoria; that many Jews died of starvation and disease before being caught up in the machinery of death.  

There are also issues subject to considerable debate. A prominent one is the question of when the Nazi leadership decided that the Jews should be exterminated. Was it in 1941, in 1939, or was it always an essential part of Nazi doctrine, only waiting for the right moment to be enacted?  On the one hand is the obvious fact that it was only in the fall of 1941 that the Germans began to kill Jews in a systematic manner. Before that there was plenty of persecution and violence but with the invasion of the Soviet Union came a qualitative change in Nazi policies.  In the thirties their persecution of Jews in Germany and then Austria was directed and putting pressure on Jews to leave. The considerable violence that accompanied it did not take the form of systematic extermination. In other words it was a classic example of ethnic cleansing.  At the end of 1940 they reversed course, blocking the flight of Jews from areas under their control.  By the end of 1941 the policy of extermination was in full swing and it formed a sharp contrast to what had preceded it.  On the other hand are the numerous writings and speeches by Nazis speaking of the need for the elimination of Jews from the world - a natural corollary of their belief that the Jews were the primary source of evil in the world, not so much subhuman but an anti-human parasitic element;  a cancer that fed on, corrupted, and in the end destroyed all societies that it touched.  Other debates include the relative roles played by the organized formally Nazi organizations like the SS apparatus and the traditional German civil and military bureaucracies; the relationship between the eschatological antisemitism of the Nazis and the much milder racism that was espoused to one degree or another by most Germans; was the Nazis' antisemtism a source of their popularity or were they popular in spite of it... There are many such debates that will probably never be definitively settled, though varying degrees of consensus may be reached.

There are also details that are revised in light of new evidence - e.g. shifting the number of Jews killed in the mass executions of the early stages of the Holocaust vs. the numbers gassed in the death camps, the support by academics, specific policies in individual countries or ghettos. Nazi Germany was a highly bureaucratized modern state and it left behind an enormous pile of documents; since 1989 the archives of Eastern Europe have become much more accessible.

What is Holocaust Denial and why is it criminalized in Europe?

Holocaust denial is the rejection of the basic facts discussed in the first paragraph below the fold. Those facts are not subject to debate anymore than, say, that there was an attack on Pearl Harbour on December 1941, that the earth is not ten thousand years old, that the moon is not made out of cheese. That historians therefore have absolutely no inclination to debate those who deny those facts is not a refusal to allow for a free discussion of historical events but rather the natural feeling that there is no reason to engage obvious nutballs.

But, you might ask, why criminalize such statements?  Nobody goes to jail for putting up a website asserting that the moon is made of cheese, if a politician said so we'd be a bit worried about his sanity, but we wouldn't see him as morally abhorrent.  The problem is that unless a person is genuinely clinically insane, the delusion known as Holocaust denial is virtually automatically tied to racism. That's because it requires the person claiming that the Holocaust is a myth to come up with an explanation of why all experts in the field reject  their beliefs as utter nonsense, why politicians in Europe and North America all accept the Holocaust as historical fact. The reaction to that reality is generally that they're all in thrall to the Jews, that indeed the Jews secretly control all Western governments and universities. An example would be the Iranian president's recent remarks, another, or for a no holds barred version go here.  And that's racism. Europe makes racist speech a crime, and as Holocaust denial, even when not initially motivated by racism, almost inevitably leads to racist beliefs, it is illegal as well. One can argue that freedom of speech should be absolute, that racists should be allowed to express their beliefs as they can in America. I would support that, but one cannot simply single out the ban on one specific form of racist speech.  Nor is it fair to draw a strict analogy to Turkey's restrictions on speaking about the Armenian genocide. Yes, both are restrictions on free speech, but there is a difference between making lies illegal, and criminalizing the truth, between laws against racist speech, and laws against anti-racist speech.

Note on survivors' memoirs

Most popular knowledge of the Holocaust rests on the experiences of survivors. The stories are human ones, not the impersonal, dry accounts based on bureaucratic memos. They also satisfy a certain need for at least a partial happy ending - among the horror recounted, at least some survived. Unfortunately the experiences of survivors is generally not representative of the Jewish experience in Nazi occupied Europe. I'm not referring so much to the fact of their survival - though there is that, but to the way in which the experience of a survivor was mostly non-typical. Thus, for example, when we think of the Nazi death camps we think of the memoirs written by Auschwitz survivors.  The problem is that what they survived was not the Auschwitz death camp (Birkenau) but the concentration camp. The latter was a slave labour camp where prisoners were held under such appalling conditions that they generally died within a year of arrival, but some lasted longer - a matter of luck, physical endurance, and resourcefulness. The death camp proper was a simple death factory - you arrived, were herded to the `showers' (the gas chamber', died, and were then cremated. There were several such camps, and with the exception of Auschwitz none had an attached concentration camp.  The only survivors were a handful of slave laborers in Treblinka who managed to grab some guns from the guards and stage a revolt.  Some escaped, a few of the escapees survived the war. Most survivors lived through the Holocaust either in hiding or passing as Aryans, an even more atypical experience than that of the former concentration camp prisoners.