It depends, I suppose. I don’t know much about this person…and a quick wiki search reveals : “A controversial figure who had an ambivalent relationship with the Church authorities, he accepted the authenticity of the antisemitic Protocols of the Elders of Zion.[2]”
So, pointing out that he accepted the authenticity of the “Protocols of the Elders of Zion” isn’t stating something that no one knows…it’s evidently public knowledge. Your job would be to present that objectively…understanding what is “antisemitic” about these Protocols and understanding Fr. Fahey’s actual position in relation to that particular aspect of such…and presenting what that means in an objective manner.
Without knowing what the Protocols really are and without knowing to what degree Fr. Fahey accepted them, I don’t think it would be fair to say that he publically advocated anti-semitism. Perhaps there is much more to his history than wiki is putting out there? Like I said, I don’t know much about him myself.
Rather than being concerned with detraction in thise case, my focus would be on avoiding calumny (also in CCC 2477).