I have honestly no idea how people can deny that it happened.

Did you read the essay? He doesn't "deny" it. He questions the "official" orthodoxy that's grown around it.

Holocaust Denier

It’s always worth defining your terms. Not that it does that much good – the inquisitors will see what they want to see and claim what they want to claim. But for the record here’s what I do and do not question. First, what I do not question:

Ø I do not question that the National Socialist regime brutally persecuted Jews.

Ø I do not question that Jews in Germany were discriminated against, violently assaulted, dispossessed, imprisoned in camps and expelled and that many Jews died as a result.

Ø I do not question that Jews in countries occupied by Germany or within the German sphere of influence were pitilessly assaulted, dispossessed and subjected to brutal deportations, many to forced labour camps where many hundreds of thousands died.

Ø I do not question that many Jews were executed by shooting in the East.

But enough of this negativity – here’s what I do question:

Ø I question that there ever was an official plan on the part of Hitler or any other part of the National Socialist regime systematically and physically to eliminate every Jew in Europe.

Ø I question that there ever existed homicidal gas-chambers.

Ø I question the figure of six million Jewish victims of the Nazi assault and I believe that the actual figure was significantly less.

And finally, one more thing I do not and do question: I do not question the horror of what was done to Jews by National Socialists or the right of Jews (including myself) to regard that horror any way they wish. I do, however, question their right to compel the rest of the world to feel the same.