I don’t think his critics deny that he was a Jesuit priest. I know that some Traditionalists think he was an opportunist and others approve of him. I don’t know.
My criticism is that his historical work is only credible on the basis of unnamed sources. The Keys of This Blood was very interesting and timely when it came out. But you can’t confirm anything. That is one criticism that I have that is unrelated to his sterner critics who seem to want to accuse him of unfaithfulness to his vows. Another is a tendency to sensationalism, again claimed without reference to verifiable sources. If he claimed that there was some kind of Satanic ritual in the Vatican back in the 50’s, we need more than just his word for it. Part of the problem is that his “fans” take Windswept House which is a work of fiction as reflecting history. He never to my knowledge issued any disclaimer. Finally in his book on exorcism, I was disturbed with picturesque descriptions of lewd and perverted behaviors which I don’t doubt are associated with demonic possession. If anyone should read it, I don’t think I am among them. It was very readable, even inspiring in showing the victory of Christ over evil, but I had to put it down. I don’t recall, maybe it had some kind of warning in the book about the language and graphic descriptions. If so, I think it should be heeded by most of us
Overall, I am dissatisfied enough with these difficulties that I have taken his books out of our parish library. Assuming that the stronger criticisms against his character are unwarranted, I don’t find him to be a reliable source for understanding the issues in the Church which he tried to address during his day.