You're right, but he's taking about a particular style of writing for a specific audience. His "rules" seem reasonable enough within that context. The passive

You're right, but he's taking about a particular style of writing for a specific audience. His "rules" seem reasonable enough within that context. The passive voice prohibition is more of a lazy pedagogical tool than sound style advice. Nothing wrong with using it, but it's often used poorly, and it's easier to say don't use it at all than to explain how to use it well. My favourite "style guide" is Clear And Simple As The Truth: Writing Classic Prose by Francis-Noël Thomas & Mark Turner, which takes the time to explain what it means by "style" and has almost nothing to say about passive voice and adverbs.