In an article for Arabi21, Massad strongly indicates that he subscribes to the discredited Khazar theory. While it is not the main point of his article, he writes, "The Zionists of European Jews claimed that they are the descendants of the ancient Palestinian Hebrews and that their settlement project is nothing more than a 'return' to their ancient country, Israel....The pan-Jewish nationalism of European Zionism, which sought to re-establish the glories of the 'Jewish' kingdoms of the Palestinian Hebrews (who were appropriated by the Zionists as ancestors of Europeans who had converted to Judaism), was portrayed as 'progressive' and socialist."
This is similar to what he wrote in English for Electronic Intifada in 2017, saying that European Jews were converts to Judaism.
The Wikipedia entry on the genetics of Ashkenazic Jews shows that nearly all studies find their origin is in the Middle East. So Massad, in the 2017 article, makes his argument that most European Jews as converts by calling it "an established historical fact."
That is "proof by assertion."
The usual version of the theory that Jews are converts is the Khazar theory, which has also been repeatedly debunked from genetic, historical, linguistic and other perspectives. It is embraced by Palestinians because their entire claim of indigeneity is destroyed when another people were there first and most Palestinian Arab families proudly trace their ancestry to Arabia. (The Palestinian Christians, on the other hand, seem to be descended from Jews.)
Since the truth is not on their side, they need to push the Khazar lie. And that lie is meant to say that Jews don't have any historic ties to the Jewish homeland.
Denying Jewish history is just as antisemitic as denying the Holocaust.
