What is the passive voice really about? We might say it's about agency. When the agent is unknown, implicit from the context, or de-emphasized, the passive voice might be preferable:

"He was arrested nine times before the age of twenty."

"I've been shot!"

"My house was destroyed by hurricane Katrina."

These sentences will usually be preferable to their active forms. "The police arrested him nine times..." "A bullet hit me..." "Hurricane Katrina destroyed my house."

We might also think of the passive voice as describing what happened to the subject. In other words, "I've been shot" answers the question, "what happened to me," whereas "the bullet hit me" seems to be an answer to the question "what did the bullet do?" So what the passive voice is really about is perspective. Peter Parker was bitten by a spider, because the story is about Peter Parker. A spider biting PP would make the story about the spider.

Note too that these sentences can be vivid: "I've been shot!" is the reactions of someone who's been shot. "Somebody shot me" sounds like a periphrasis. With effective uses of the passive, nobody will complain about a lack of immediacy.

Notice that the passive voice is not invariably vague or evasive about agency. It can even make agency emphatic. "Yes, you were bitten by a dog, but I was bitten by a hyena." With the "He was arrested..." example, anyone would understand that it was the police, so there is no real evasion there. If you recast a passive sentence in the active, and come up with a word like "people" or "somebody," you know the reason why it was put in the passive voice in the first place.

Composition classes aim to enable students to write in an academic style and those succeed in college. These same classes often discourage the passive voice; yet academics themselves, especially social scientists and real scientists, love to use the passive voice. Students who write with a lot of passive verbs do so because they are emulating academic writing. They may be doing so ineptly, but that is what they are doing. The answer is not to discourage the passive voice, but to demonstrate its multiple uses.