"Dull to read" is a subjective evaluation I don't share. Moreover, it is exactly the sort of justification which is given (1) to arbitrary norms. When people are told (2) that they shouldn't do X, they easily convince themselves that X feels dull, even if there wouldn't be such a feeling without the (arbitrary) social norm. I don't know for certain whether this is the case of the passive voice, but I am generally skeptical about subjective justifications of existing norms. As for obscuring reality and the Orwell's essay, see Vladimir_M's comment and the links included therein. One of the more interesting points is that the critics of passive voice generally don't use passive voice less often than the rest of the writers. Maybe I have been careful in this comment and thus am not entirely fair, but I have used passive constructions twice (numbered above) in positions where the active alternative would be much longer, while in the parent comment you have put three instances of passive voice ("justifications are attached", "link is explained", "mention is thrown"; two of them only to spare a short personal pronoun "I"). "Metaphysics of metaethics" is indeed confusing for me, but I usually don't understand anything containing the word "metaphysics", so I am not sure whether the alternative is any better. I agree with your objection to "shocking" and, to a lesser extent, "dissent". No problem with "needless to say".

Passive constructions change the focus. Sometimes they're better. It's only when they're used to obfuscate lack of specific evidence that I object. It's advised to mix in some passives when describing research, at least.