Well, Sowell would approach it from an economists' view, wouldn't he?
He might be right, but the lack of assimilation is far too important. A perfect example of this (and supporting Sowell's thesis) is medieval Spain. When the Spanish expelled the Moors, they viewed the Jews (who played the middleman role, often) as collaborators. Jews form an independent culture and when there are nationalistic movements, they are the most obvious outsiders, until recently because they had noplace else to go.
Consider the term Anglo-Saxon. There are no Angles and no Saxons anymore.
I like Sowell a lot and do not doubt his description of the historic role of the middleman as applied to the Jews. Problem is, the arabs were also middlemen for centuries, managing trade routes across the deserts, up and down the coast of the Hijaz, and the Mediterranean. But suspicion or resentment of the middleman does not reach the historic dimension of attempted genocide.
One ancient accusation against the Jews is that they treated each other by mosiac law differently than they treat gentiles. Much like the way arabs are supposed to favor each other vs the way they treat non-arabs, carried over into Islam when it gained ascendancy. I don't know how much truth there is, or ever was, to this.
That theory's been kicked around. In addition to markets for trade goods, Jews also helped create capital markets, because Islam and Christianity have at various points in history, forbidden or at least looked askance at lending money for interest.
This was fed by the spread of the Jewish diaspora, particularly in parts of Europe and the Muslim world that sat astride trade routes; and further driven by the fact that European craftsmen's guilds often barred Jews from joining.
Any time you have a people apart, who are seen as having a secretive and poorly-understood role in "the system," you have a ready-made scapegoat shen the system breaks down.
These things also form their own inertia; various despots turned blame to the Jews to take the heat off themselves (notably the czars), and once that body of literatire gets started, anyone looking for a scapegoat has a head-start. It's not a coincidence that the Protocols keep coming up in new translations or that modern-day Muslim anti-semitism borrows heavily from the Julius Streicher playbook.
David Irving used to be -- with emphasis on the past tense -- a fairly respectable historian. But I think at over his years of researching and writing about the Third Reich, something like the Stockholm syndrome took hold, and he bekame a kool-aid drinker rather than an objective researcher.