Well, I'm all for turning the other cheek. I like few words and letting your yea be yea and your nay/nay. When you say that it contains slander, well, maybe yes. But, slander does not necessarily mean incorrect or untrue. Consider Jesus addressing the religious charlatans of that time (i.e. "you vipers"). They hated Him for it. They were blinded by the devil, the world, the flesh and, were more concerned with how they looked in others eyes than in God's.
Such accusations against the RCC may (or may not) be true, but they do little to prove or disprove Rivera's case that he really was a priest. And if he wasn't really a priest, his whole conspiracy charge, based on his supposed first-hand knowledge, experience, and access to insider information as a priest, falls completely apart. If his foundational argument (having been a priest) is a lie, who's to say what's built upon it isn't a lie as well? The proof of the conspiracy is founded upon his first-hand knowledge as a former priest. No priest = no proof.
Any defense of Rivera needs to be made for his own credentials, not against those of his opponents.