@InfraBlue,
If Netanyahu had stuck to the historical facts without exaggerating, he could have hit a rhetorical home run.
After all, the comment was made in the context of Arab violence against Jews said by the Israeli authorities to have been stirred up by the lies of Arab propagandists as to Israeli plans for shared holy sites in Jerusalem. And indeed, al-Husseini did the same thing using the issues of the Dome of the Rock and al-Aqsa in Jerusalem.
Of course al-Husseini wasn't the inspiration for the Holocaust. Its possible that the Ottoman Turks were, indirectly and through historical example. Hitler is reported to have said "Who now remembers the Armenians?"
But it's true that al-Husseini spent the war years in fascist Italy and Nazi Germany; that he was active in urging that Sephardic Jews (including children) from the Balkans were not spared extermination; that he recruited SS regiments for the Nazis from the Muslims of Yugoslavia, who guarded the security of railway lines carrying Balkan Jews to Auschwitz, and that one such regiment took an active role in the extermination of Jews, Serbs and Gypsies in Yugoslavia as part of special operations units. Finally, it's true that al-Husseini was a personal friend of Himmler and took a tour of Auschwitz as his guest.
According to Dieter Wisliceny, senior SS officer and a key executioner of the Final Solution:
"The Mufti was one of the initiators of the systematic extermination of European Jewry and had been a collaborator and advisor of Eichmann and Himmler in the execution of his plan... He was one of Eichmann's best friends and had constantly incited him to accelerate the extermination measures. I heard him say that accompanied by Eichmann, he had visited incognito the gas chambers of Auschwitz."
(Cited in The Politically Incorrect Guide to the Middle East, by Martin Sieff)
Now perhaps in historical retrospect, some of this was just the Mufti tooting his own horn, and passed along uncritically by Herr Wisliceny.