I studied this period of French history with Roger Williams, a noted historian of the Second Empire (his best known book was Gaslight and Shadow: The World of Napoleon III) and Third Republic (he published an anthology on the Dreyfuss Affair). His view, which seemed pretty well thought out to me at the time, and which I have no reason to doubt, was that while anti-semitism may not have triggered finding a scapegoat to protect the actual criminal (though some evidence suggests otherwise), certainly was the reason the Affair took the course it did.
Before I'd dare contradict your teachers I'd want to read a lot more about the affair.
An analogy, perhaps flawed, that comes to mind, is that of the fate of J. Robert Oppenheimer. The official version, of which much has been made, was that he was the subject of a witch hunt during a time of hysteria about American Communists. Left unsaid is that at the time the Army and Air Force were wrangling about which service should control our nuclear arsenal, and which defense contractors should stock it. JRO had stayed with the army after the air force was spun off and was seen as being the army's ranking scientist or close to that; all his detractors, (Bethe, Rabi and Teller) who testified against him were air force men, his defenders army men. While the words spoken on Capitol Hill were all about the political theories of a man versed in nuclear physics and Hindu vedas, the unspoken battle, which historians by and large ignore, was about which keiretsu should arm us with fissile materials.
The idiocy of the entire Dreyfuss trial, and the absurdities to which the French army went, makes me suspect something similar was afoot. I feel that somewhere in that courtroom, there was an elephant.