That's the first time I've seen a legitimate argument for avoiding the passive voice, rather than the usual 'oh it's a bit confusing'. Of course, this argument falls down if the subject of one's passive construction is a person rather than an abstract concept, e.g. why should one automatically prefer 'the Spartans attacked the Athenians' over 'the Athenians were attacked by the Spartans'. And I do think that to banish the passive voice altogether is to lose something from the richness of the language.