I think we should make a distinction between facts and truth. What you said about scientific mentality isn't really relevant here. Holocaust was a historical fact. So saying it happened is different from proposing a theory about say a particular mechanism. Actually one way to refute theories is by experimental evidence, and although the interpretation of what an experimental result actually means is itself partly based on the existing still reliable theories (reliable in that particular case), the fact something has been observed or a change has taken place is there.
There is every evidence that Holocaust did take place. There are films, photos, documents and witnesses from different nationalities and political orientation.
It is a fact, why is it denied, where as many other facts of everday life are taken for granted with much less "evidence".

As for Holocaust deniers, again let's compare it with other similar cases. There has been many genocides commited throughout human history against different groups of people, and although the perpetrators of the crime themselves usually deny the accusations like Turkey in the Armenian massacre or the Arabs right now in the case of Sudan, it is very rare for third parties, people who belong to neither side of the affair and in later times to deny so energetically and so blindly any other event with comparible magnitude. Why is the Holocaust different? That's my question.

Antisemitism is quite a common attitude in different degrees and it is not just about the "Jews" despite its own claims. Mostly it comes in mild doses among people who are otherwise normal, but it is there nevertheless. It even exists among the Jews although there the number is very limited for obvious reasons.
I think it shares a lot with say anti-West or anti-Capitalist attitudes. (the latter is rampent among the Jews too which is an important point, since now the direct attack against one's ethnicity is replaced with a more subtle and abstract and less personal target.)

I don't think banning Holocaust deniers' works and speeches is a good idea either. It violates the principle of free speech and it only adds to their aura of being victims for their couragous struggle for freedom against sensor. Where as refuting the evident nonsense they claim is both easy and useful for keeping the debate and the memory alive in a natural way, without falling into repetitions or cliches.

However that doesn't mean that I can feel respect for such people for even a second.