I'm a Jew and I can at least feel some begrudging respect for neo-Nazis who openly admit the Holocaust happened and was a good thing. But the ones who claim it was all made-up, or who even claim it was exaggerated, are so low-IQ and/or dishonest that it's embarrassing.

One reason it's so stupid is that if you took every disbeliever and somehow persuaded them it was all true, not a single one would go "oh, it was a mistake for me to adhere to National Socialism, I believed the claims were all lies because it's not good to murder millions of civilians solely due to their heritage and surely the Nazis weren't so evil and the accusations must be enemy propaganda". No, they would of course just say it was good.

But then why deny it in the first place?

"I know it's real but I falsely claim otherwise in public because it's effective propaganda" at least provides an explanation beyond mental retardation, but if that's what you're doing, is that behavior not more malevolent and manipulative than anything Jews as a group or even as individuals have ever been accused of? Do you even think that way about many anti-Jewish accusations; saying the accusations are real while knowing they're not? Where does the honest belief come in?

There are many different categories of evidence proving the intent and near-successful attempt to kill all the Jews in Europe, but the simplest is the recording of the Posen speeches: https://en.wikipedia.org/wiki/Posen_speeches

>"I am now referring to the evacuation of the Jews, the extermination of the Jewish people. It's one of those things that is easily said: 'The Jewish people are being exterminated', says every party member, 'this is very obvious, it's in our program, elimination of the Jews, extermination, we're doing it, hah, a small matter.'"

Your only options are to say the recordings are an impersonator or that at the very least, the SS wanted to perpetrate the Holocaust and believed they had successfully perpetrated most of it.