Part of the problem, if my school experience gives any indication, stems from confusion about what, exactly, passive voice is. Many of my teachers told us to avoid any form of the verb "be", and some even had us memorize a list of its various forms—I can still rattle off "am, is, are, was, were, be, being, been" without even thinking about it—as part of the effort to avoid it. At least one took it a step further and gave instructions to avoid words like "exist" and "become" as well! Even at best, though, looking for "be"s at most serves only as an aid to finding passive voice, not the definitive identification it was sometimes treated as. Not until taking college courses on the Japanese language (which has a verb ending specifically for passive form that gets regular use) did I correctly understand the concept of passive voice.