I aways took the aversion of English speakers against the passive voice as a sign of linguistic incompetence. Instead of teaching students how to write well on the passive and active voices, they prefer to reduce the language to its minimum denominator. The confirmation is in [1]: many journalists and writers don't even know how to define the passive. It is a sad thing to watch. [1] http://www.lel.ed.ac.uk/~gpullum/p…
The bigger lesson, which students who keep working at writing learn, is to be aware that active and passive exist and that it's worth keeping an eye out for sentences that read better with one or the other.
But, for whatever reason, high school students use way the fuck too much passive voice, and they use it inappropriately. If the only rule you can get them to internalize is "stop using passive voice", that helps a ton. It stops being a "rule" if you know what you're doing, but they don't.
Source: I'm close with a few English teachers, and with some authors.