What "Anti-Catholic pseudo history" is being promoted by Secular Humanists?
Visit any internet discussion by "Rationalists" and you'll find the whole gamut.
The Conflict Thesis, "Christian Dark Ages", "destruction of pagan learning", "Christmas/Easter is Pagan", Great Library of Alexandria, forms of the Black Legend, etc.
Basically anything about pre-modern historical Christianity commonly discussed by "New Atheist" types.
Regarding Hitler, I have stated in many threads that he used the teachings of (Protestant) Christian leader Martin Luther to inflame Christian (Protestant and Catholic) Germans against the Jews. Hitler united Catholics and Protestants in accepting the "Final Solution".
Catholics: famously impressed by people referencing the theology of Martin Luther
While Christianity did help create an undercurrent of anti-semitism in Germany, it was not the source of the Scientific Racialist anti-semitism promoted by the Nazis.
Luther was a theological anti-semite, Hitler was a racialist anti-semite. His anti-semitism was minimally, if at all, influenced by Luther.
Nazis did use Luther's words to help justify their racial anti-semitism, but there were many other things (at least most of which were far more important): Racialist "Science", anti-Marxism, WW1 'stab in the back', avaricious exploiters of 'real' Germans, etc.