The passive voice allows us to posit ideas and scenarios in ways that are open. They allow for a multitude of people to be both cause and effect in the scenario. They turn the focus away from the individual and towards the idea at stake. The rejection of the passive voice is the rejection of possibility, openness, and imagination.
Compare these statements: “X could be understood in terms of Y” rather than “X is a function of Y,” These appear to be very similar, but they have very important distinctions. The latter is certain and definite, while the former allows for interpretation, disagreement, caveats and qualifications. While some scoff at this as weak hedging, I steadfastly maintain that there is a general value in allowing others to build on an interpretation. Moreover, the more we are inclined to think and speak of the world in definite terms that do not permit multiple interpretations, the more difficult it is for our minds to face situations of disagreement and multiple perspectives. I think our language has developed an active and passive voice as a reflection of the understanding that some parts of our reality are objective and concrete while others are subjective and abstract. (Also, there are times that we want to focus on the actor and there are times that we want to call attention to the action.)
Though there are many inappropriate uses for the passive voice, it is dangerously narrow-minded to instruct students to simply avoid the passive voice without properly explaining why. I use the passive voice often when writing because it serves my goals for the type of writing I tend to do. Without an understanding of what the passive is and why it might be useful, I could not make a deliberate choice either to use or not use the passive voice. To truly allow someone to choose not to write passive, they must be taught when and why they should write passively.