A quotation from Warrant for Genocide. Cohn is writing with particular reference to the work of Augustin Barruel.
"No time need be wasted on the claim that the French Revolution was produced by a conspiracy reaching back to the fourteenth century. As for the obscure German group known as the Illuminati, they were not Freemasons at all but rivals of the Freemasons and had in any case been dissolved in 1786. Further, the role of the Freemasons was also fantastically oversimplified and exaggerated. It is true that the Freemasons shared that concern for humanitarian reform which is commonly associated with the Enlightenment - for instance they contributed to the abolition of judicial torture and of witchcraft trials, and to the improvement of schools. On the other hand at the time of the revolution most Freemasons were Catholic and monarchist - indeed King Louis XVI and his brothers were all Freemasons; while during the Terror Freemasons were guillotined by the hundred and their organization, the Grand Orient, was suppressed....
Barruel once remarked that if the Simonini letter [a document alleging that the Jews were behind the supposed Masonic conspiracy] were published it might provoke a massacre of Jews, and on that occasion he was talking sense; for in embryo the letter does indeed contain the whole myth of the Judeo-Masonic conspiracy. But the letter also points very clearly to the circumstances which gave birth to that myth. Needless to say it had nothing to do with the real relationship between Jewry and Freemasonry, which was tenuous. In the eighteenth century the Freemasons were on the whole hostile to the Jews (and so, incidentally, were the Bavarian Illuminati). At the time of the Simonini letter many lodges were still reluctant to accept Jewish members. At no time have Jews, or persons of Jewish descent, played a disproportionate part in Freemasonry. These are the sober facts. But facts such as these have never deterred anyone who wished to believe in a Judeo-Masonic conspiracy. Had not Barruel shown that the French Revolution was the work of a conspiracy of Freemasons? And had not the Jews benefited from the revolution? No more was required to establish that Freemasons and Jews were closely associated, in fact practically identical.
It is true that the French Revolution, like the American Revolution before it, really did help the Jews. Since it proclaimed 'the rights of man' and championed the principles of liberty, equality, and fraternity, it was logically bound to grant civil rights to French Jews.... Those who identified themselves with the ancien régime had to account somehow for the collapse of a social order which they regarded as ordained by God. The myth of the Judeo-Masonic conspiracy supplied the explanation they craved."