Is it wrong to write in passive voice?

It may be considered "weak" but never wrong as long as it's constructed correctly. However, as many of these answers imply, there are "good/better/best" contexts for the use of passive voice. Here are two specific contexts that will be helpful to many students: SAT questions & news writing.

The official SAT practice book refers to the "weak passive verbs." These are found in Sentence Improvement questions. Most of the time, a straight forward active voice answer choice is a better answer than a weak passive voice answer choice. (However, in the last decade, I have seen some real tests questions with a passive voice answer as the best answer, so don't automatically assume it's wrong.) Generally, it's also best to use active voice within SAT essays.

Traditionally, news writing requires the use of Subject-Verb-Object sentence structure. This is inherently active voice. Passive voice in news writing is usually either found in a direct quotation or in reporting information that is not complete.

Lastly, be sure that you fully understand the construction of passive voice construction. (It's not just the feel of the sentence.) The object is moved to the subject position and the verb becomes a participle with a to be helping verb. Here are two examples of passive voice based on rearranging this active voice sentence: Bob ate all the cookies. (S-V-O)

(1) All the cookies were eaten.   (O-V  The object is now the subject, and we don't know who did it.)
(2) All the cookies were eaten by Bob.   (O-V-S  The actor is now an object and less central.)

I would not say that passive voice is "wrong," but active voice is usually stronger, especially for an English paper. When I worked with students at my university's writing center, I usually advised them to use active voice because it emphasizes the subject rather than the object. That being said, lab reports in psychology or hard sciences usually require passive voice. Agreeing with the previous posters, your best bet would be to stick to active voice whenever possible.

I agree with the statement below regarding passive voice.  Passive is often used in official writing, like that of the government or business.  It is primarily used when the speaker/writer wants to empasize the result of an action, rather than who or what is doing it.  For example, in old adage, "Children should be seen and not heard," it is the result of the action that is important, not who will or will not see or hear the children.  It is important, though to know how to effectively use the passive voice in more advanced writing, like essays or research papers.

Writing in passive voice is not wrong, it is simply not usually the prefered form of writing. Reasons are:

(a) it is not direct,

(b) it is usually wordy and redundant,

(c) it is not as clear nor as positive as active voice.

Follow your teacher's instructions on this. Usually s/he will accept a combination of passive and active.

The passive voice of a verb is acceptable in some instances: 

1) If the doer of the action is unknown. Example: The United States is regarded as the most democratic nation in the world. 

2) If the receiver is more important than the doer.  Example: Clamshells were used by some Native Americans as money. If the writer's topic is clamshells, then the passive voice is correct.

3) If the writer decides that it is best to not identify the doer. 

It is also a matter of tone.  Passive is usually good when you don't want to seem confrontational or too aggressive especially in an interpersonal or relational context during conflict or problem solving.  The active voice reflects or suggests more assertiveness or can be too accusatory. 

"I" statements in the active voice can be used to acknowledge more personal responsibility for actions in a relational context.  Just as "You" statements may be used to assign blame or responsibility besides self.

Example: "I crashed into a car at the stop light." (Active)

vs.

"The car was hit by a driver in front of me who wasn't paying attention at the stop light." (Passive)

An arena of writing in which it is often improper (though not necessarily wrong) to use the passive voice is in screenwriting.  That may not be all that pertinent to the topic at hand, but I figure it was worth mentioning.

I'm one who tends to prefer the active voice.  Of course, I'm also one who typically writes argumentative position papers, and there the active voice is hugely important in one's presentation/critique of an argument.

Like everyone else has said, using the passive voice isn't "wrong;" it's just that most people prefer the active voice. Again, like everyone else has said, the active voice is more succinct and more direct. Usually the reader is more interested in who does something, rather than the object of that action.

However, there are cases in which the passive voice is rhetorically helpful--that is to say, more effective when making an argument. Let's say, for instance, that you're a prosecutor for a murder trial. The tactic you've chosen in making your cases involves painting a picture of the victim, characterizing the victim in such a way that the jury finds her sympathetic and is more likely to convict the defendant. You may start by describing the victim: "Sarah Marshall was a grade school teacher. She paid her taxes. She was a dog-walker. She was a mother of three." After you've described the victim, you have two ways to go about describing her death: the active voice ("He murdered her") or the passive voice ("She was murdered by him"). The active voice is fine, and even helpful, because it immediately connects the defendant to the act of the victim's murder and, in its brevity, it tonally communicates the brutality of the act. However, it also renders the victim--who, up to this point, was the subject of the argument--an object, thus placing her in a less rhetorically powerful position. The passive voice, in this case, highlights the tragedy of her death, because it places her as the primary focus of the sentence while immediately connecting her with a brutal death. In fact, because it's in the passive voice, the victim seems helpless; the murder happened to her, and she wasn't really involved in it. With the passive construction, the jury would keep the victim in mind, which (if the victim is particularly sympathetic) might help you win your case. 

Active sentences are generally more interesting, but there are a small number of instances in which using the passive voice makes more sense. For example, "I've been shot!" is much better than "An unknown assailant shot me" when you want to emphasize the fact that the main character has just been shot. In this case, the most important person in the sentence is the victim, not the unknown shooter.

Later in the story, it might be more important who did the shooting and then you might write instead, "Harvey shot me!" In that case, an accusation is being made and therefore it is the shooter who is the most important person in that sentence. (Notice that I said "an accusation is being made" instead of "someone made an accusation." I did that because I wanted the emphasis on the accusation and not the accuser.)

Most of the time you will need to use active voice, but if you find a sentence in which using active voice doesn't sound right, do this. Ask yourself, where does the emphasis belong? Who or what is the most important thing or person in the sentence, given the context?

The use of the passive voice is not by itself wrong. It's a matter of style and clarity. When you use the passive voice, the message can be less clear, confusing, or vague. As a result, most English teachers will tell you to use the active voice; they are, after all, trying to teach you how to be clear in your writing. Using the passive voice can be effective, for example, if you are focusing on the action and who did the action is not important. The hard part is knowing when to use it.

A newspaper journalist may employ the use of the passive voice in writing an article to shift the focus of the doer of an action to a less important status to focus on that action/occurrence or because the writer is unsure of who performed that action.  This response speaks more to the particular genre of writing where one may realize the use of the passive voice.

passive and active forms of the same sentence are structurally (syntax) different while conveying the same meaning (semantic). Really, it is an arbitrary matter of preference.  However, it's not so "arbitrary" when it's your boss (or teacher) telling you which they prefer.  A more accurate response to your question would require more context.

Lisa A. gave a succinct and accurate assessment.  I just want to emphasize that it depends on the type of writing you are doing as to whether you use active or passive.   

It is not wrong to write in passive voice unless your grade depends upon writing in active voice.  If your teacher is teaching you to write for a standardized test, he or she likely wants you to stay in active voice.  Active voice is more interesting, more effective, and often easier to read.

Using the passive voice is not "wrong" but it is often not effective, especially in telling a story. It leaves the importance of the people involved in the action expressed vague. For instance, "Charlie bit me" (active) might be the beginning of a powerful story about the writer/speaker and Charlie, but "I was bitten by Charlie" (passive) leaves the reader/listener wondering if Charlie is important at all in this situation. The most interesting continuation of "I was bitten by Charlie", to me, would be "this time." In which case we have the beginning of a very different story, about the writer.   Hmmm.

When using the passive voice, the writer must be aware that s/he might bore the reader.  If the reader falls asleep, upon wakening, the reader may want to do one of several of these things: 1. rip up the book, 2. never read the author's work again, 3. re-write his essay.  Verbs, jumping, vibrating, tingling, are the stuff of making the reader sit up and read...  Another consideration for using a certain tense is this: 1. what audience am I writing for?  an audience who wants to be inspired? sleep? learn something? 

The short answer is: no,of course not.

The short answer is: it's wrong if your teacher says it's wrong. Every teacher has his or her likes and dislikes, and it's good to learn what each teacher wants and give it to them. That is what will give you higher grades. If your teacher doesn't care and it's up to you, remember thses things: In general, passive voice uses more words to say the same thing (this becomes important when you have word limits on what you're writing). Also keep in mind that the noun or pronoun that leads the sentence gets more emphasis. For instance: "The dog caught the ball" versus "The ball was caught by the dog." The second sentence has more words and the emphasis is on the ball.