The astroturf is greener on the other side

While Marshall does not deny the promise of Christ to be with the Church, the alleged success of the endless conspiracies and infiltrations he recounts are sufficient to undermine any reasonable confidence in these promises, or at least to confuse inessentials with the essentials which are guaranteed—which amounts to the same thing. To his credit, at the end of the book, the author considers the various responses we might make to his extravagant claims, and he rightly concludes that any proposed solution which suggests that the Church does not remain intact, or that we no longer have a true pope or true cardinals and bishops, must be rejected in favor of simple resistance to the evils that now appear to dominate the Church. But he is unwilling to allow even those modern popes who have already been canonized to instruct him or his readers on what the key evils are. Instead, he must cling to his private judgment, his conspiracies and his plots to prove that everything he personally dislikes has arisen through a devious orchestrated manipulation by particular evil groups.

https://www.catholicculture.org/commentary/articles.cfm?id=773

That's an ironic and trenchant observation. But what Mirus fails to take into account is that this reflects the bitter disillusionment of a convert. For instance, it's surely not coincidental that Marshall used to be an Episcopal priest. Dismayed with his own denomination, he thought he was escaping that mess by switching sides. But he walks smack into the same mess ahead of him, in the road to Rome, that he thought he put behind him. During the puppy love stage of his conversion under Benedict XVI, he was blind to the same currents coursing through the church of Rome. But the Francis pontificate has exposed all that and accelerated the trends. Marshall meets it coming and going. An idealistic convert belatedly mugged by Catholic reality, once the puppy love stage wore off, and the sense of betrayal kicked in.