That the Holocaust happened is irrefutable.
Holocaust deniers do not argue that there was no killing of Jews or that there were no camps.
They argue that there were less people/Jews killed than currently claimed by the majority of historians and that the details of the death camps are inaccurate.
So they do not have to bring proof, they merely have to put doubt on some of the claims of the events and actions during the Holocaust.
And you rightly point out in your last sentence: they feel!!! there was no holocaust. They feel that they are unjustly 'prosecuted', 'haunted' by those people that want to make sure that the facts of the holocaust get remembered. Some are anti-semitic and have their own racist agenda.
EDIT to Vincent Apax
There were 6 concentration camps in greater Germany:
Dachau, Sachsenhausen, Buchenwald, Flossenburg, and after the annexation of Austria in 1938 - Mauthausen, finally in 1939 Ravensbrück (for women).
There were 6 concentration camps in Serbia:
* Banjica concentration camp (near Belgrade)
* Sajmište concentration camp (near Belgrade)
* Crveni krst (in Niš)
* Dulag 183 (in Šabac)
* Svilara (Pančevo)
There were several camps in France:
During World War II, The French Vichy government ran what were called "detention camps" such as the one at Drancy. Camps also existed in the Pyrenees, on the border with pro-Nazi Spain, among them Camp de Rivesaltes, Camp Gurs and Camp Vernet. About 73,000 Jews were deported to Nazi Germany. In addition, areas which were annexed by Germany formally from France such as Alsace-Lorraine had concentration camps set up, the largest being Natzweiler-Struthof.
The most and the largest camps were located in Poland.
Concentration and Extermination camps:
Auschwitz-Birkenau · Bełżec · Bergen-Belsen · Bogdanovka · Buchenwald · Chełmno · Dachau · Gross-Rosen · Herzogenbusch · Janowska · Jasenovac · Kaiserwald · Majdanek · Maly Trostenets · Mauthausen-Gusen · Neuengamme · Ravensbrück · Sachsenhausen · Sajmište · Salaspils · Sobibór · Stutthof · Theresienstadt · Treblinka · Uckermark
In Germany from 1934 onwards, every resident had to carry an ID card and every family had to have a family book proving their Aryan decent for at least 3 generations (I still have my family's book). so it is not difficult to find out how many German Jews were killed. It was more difficult in Poland and later in the War years since the speed with which events accelerated made it difficult for the German bureaucrats to maintain correct records.
The number of people killed is not an arbitrary number, it has been established after painstaking investigation over many years.
And even if, and I say if, there were only 3 million people killed by German government officials in ghettos, camps, shootings etc, this would make no difference whatsoever.
Why is it important how accurate the details are??????
You have to ask yourself. Would a person feel any better if they killed only 500 men, women and children instead of 50,000?
Vincent Apex is incorrect
In German there is no term Death Camp only 'concentration camp' or 'work camps' for all camps that were build to either kill the inmates outright or work them to death. And in all the camps I mentioned, inmates were killed upon arrival or at the end of their usefulness.
There is a longer list of camps that were merely prisons or transition camps all over France Netherlands Italy etc.
And the fact that you are able to question the numbers killed in other genocides does not make it valid argument to question the number killed in the Holocaust. One only questions the number killed 70 years ago if one has a racist agenda, not if one wanted to find out the truth.
There is no need to mention camps across the US in this context, that is another topic.
Holocaust denial is illegal in these countries, because they suffered from it. These are countries that opposed Guantanamo Bay as well. These are countries that have signed the human rights declaration. These are countries that are actively working to prevent similar things from happening again.
Are you questioning their integrity and intelligence??