The passive voice is like any tool. You can use it well, you can use it badly, and you can abuse it right out. If I use a garden hose with a nozzle to spray water on my flowers, that’s nice. If I turn the nozzle on jet-stream and churn up the dirt underneath them, that’s bad. And if I take the hose and run over it with my car back and forth, in a fit of pique—angered by the local Gardening Society—that would be abuse.
The Passive Voice is used well when the agent of the verb is general or of no significance. See the previous sentence! It would be silly to write, “People use the passive voice well when the subject is general or of no significance,” because the subject, people, is general and of no significance. So why include it? Instead, use the Passive Voice, which in this case is more concise and more emphatic.
The Passive Voice is also used to highlight the sufferer of the verb, rather than the agent: “John, this innocent man, was beaten by these teenagers, robbed, thrown in a ditch, and left for dead.” It would be foolish for the prosecuting attorney to hide John from the jurors by tucking him into the middle of a long sentence. Put him up front! It requires the Passive Voice? Let it!
The Passive Voice helps us retain a consistent subject in a series of sentences, regardless of what’s going on with the verbs: “The old man hobbled down the alley, occasionally bumping into a wall or a back fence. He had lost his bag, and was looking for something to eat. He had been in bad scrapes before, but never as bad as this. Once he had gone a week with nothing to consume but three jugs of corn mash. In Africa he’d been riddled almost to death by mosquitoes. He’d been tracked down by posses and shanghaied by drug smugglers. Nothing as bad as this.”