Your query would require an extended answer. In this posting I provide a summary about Kant’s key role in this issue, which can be further discussed and referenced if desired. Outgoing from Kant in a next posting I will briefly outline Spinoza’s influence and the role of Voltaire.
Kant’s demolition of the Jewish religion.
In his work Religion within the Boundaries of Mere Reason (Book Three, Division Two -). Immanuel Kant wrote:
“Judaism is really not a religion at all but merely a union of a number of people who, since they belonged to a particular stock, formed themselves into a commonwealth under purely political laws, and not into a church; […] That this political organization has a theocracy as its basis […], and that therefore the name of God, who after all is here merely an earthly regent making absolutely no claims upon, and no appeals to, conscience, is respected -this does not make it a religious organization.[…] Furthermore, since no religion can be conceived of which involves no belief in a future life, Judaism, which, when taken in its purity is seen to lack this belief, is not a religious faith at all.” […Judaism is conceived] “as actually to exclude from its communion the entire human race, on the ground that it was a special people chosen by God for Himself -[an exclusiveness] which showed enmity toward all other peoples and which, therefore, evoked the enmity of all”.
Here we find those conceptions of Yahweh as “the false God”, and “the hatred of other peoples” as essential characteristics of Judaism”, which justified the anti-Semitism for generations of philosophers and theologians.
In his Anthropology from a Pragmatic Point of View (Note to §44) Kant describes the Jews as a “nation of cheaters”, a nation of merchants “the great majority of whom, bound by an ancient superstition that is recognized by the State they live in, seek no civil dignity and try to make up for this loss by the advantage of duping the people among whom they find refuge, and even one another. The situation could not be otherwise, given a whole nation of merchants, as non-productive members of society (for example, the Jews in Poland).” Otto Weininger, who can be considered an efficient propagator of the dehumanisation of the Jews, refers to this Note in the Anthropology and claims “Kant has doubtless been the sharpest anti-Semite of all.”
Moreover, Kant repeatedly praised in several works “the pure moral religion, with the abandonment of all teachings of the Old Law” as the “the euthanasia of Judaism”. Leon Poliakov has called this notion “the metaphysical form of the cry ‘Death to the Jews’”, and considers it the sign of Kant’s “deep rooted contempt” for them. Even if one accepts that Poliakov exaggerates somewhat, he seems right in that Kant defines “natural religion” as Christianity “purified” from “the Revelation of Mount Sinai”, and declares that the Jewish faith “is not even a natural religion but paganism”, suspecting that the Jews ever had “a public pure moral religious instruction”.
In any case, Kant’s claims on Judaism are more than a repetition of prejudices and stereotypes. They build up a well-reflected criticism, which radically demolishes Yahweh and the Jewish religion.
Certainly Kant was friendly towards the philosophers of the Haskala (the Jewish Enlightenment). Between Kant and Moses Mendelssohn for example there was reciprocal esteem and inspiration. However, one should not overlook the fact that it was Kant who ruined Mendelssohn’s project for a symbiosis between Judaism and the Enlightenment. Yirmiyahu Yovel points out that “in Religion within the Boundaries of Mere Reason Kant uses Mendelssohn’s work Jerusalem against the intention of its author, stating that originally Judaism is no religion, but only a body of political rules without any moral and general-reasonable content. Thereby, after Mendelssohn’s death and in a very unfair manner, Kant devastated also the Jewish part of Mendelssohn’s project.” And as a consequence Mendelssohn’s highly original contribution to the proofs of the existence of God in Morgenstunden did not receive the attention it deserves.
I do not wish to be misunderstood. I am not stating that Kant was the same kind of anti-Semite as Theodor Fritsch, or even as his admirer Otto Weininger. Kant was a promoter of human rights and has the merit of reckoning moral law among the foundations of philosophy; in no ways was he a racist, even though “race” is a rather central category of his Anthropology. What I am stressing is that it was possible to make of the Jews in Germany a foreign and enemy race, because Judaism was not granted the status of a religious faith. And in demoting Judaism as a religion, Kant’s ideas played a decisive role. These were further developed and propagated by his fellow philosopher Fichte, and were received by theologians like Schleiermacher and Lagarde among many others. Theodor Fritsch propagated Lagarde’s view that “the Mosaic law, and the embittering pride it conveys, preserves the Jews as a foreign race.” Fritsch’s perverse achievement was to make Judaism reachable to the racist dialectic, and the “völkisch” ideology became a practical and politically efficient anti-Semitism.