Passive voice seems to be the bane of every high school teacher's existence. You can certainly see why. It can't be a lot of fun to read paper after paper explaining that "The shot was made by Atticus to kill the dog and save them" or "The book was written by an alcoholic Faulkner." Surely they'd want to read something more enlivening: "Atticus shot the dog and saved them," or "Faulkner wrote the stream of consciousness story, but he often lost consciousness while drinking."
To review: In active voice, the subject of the sentence is doing the action ("I ate the hot dog"). In passive voice, the target of the action is the subject ("The hot dog was eaten by me"). As you can see, passive voice can be a lot clumsier, clunkier or even confusing in many circumstances, but it's not incorrect. Writers may also employ passive voice when they haven't done their homework, as in, "The man was shot and killed on Thursday." By whom? Hmmm, not sure. As with most things, the key to passive voice is moderation. (Someone should've told Faulkner.)
And sometimes we must use it. In some professional writing, it's considered a good way to write objectively. For that reason, you might see studies or scholarly work that uses passive voice to say something like, "The experiments were conducted according to strict standards" as opposed to "We conducted the experiments according to strict standards."
So watch for passive voice, but don't buy that you're a grammar pariah if you use it.