Wikinews policy is that all articles should have a neutral point of view. According to Wikimedia founder Jimbo Wales, NPOV is "absolute and non-negotiable" (for Wikipedias).
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The neutral point of view policy states that one should write articles without bias, representing all views fairly.
Neutral point of view means that an article should fairly represent all sides in a news story, and not make an article state, imply, or insinuate that any one side is correct. (Of course, there are limits to which points of view are worth mentioning, and this can be an area of conflict.)
It is crucial that Wikinewsies work together to make articles unbiased. This comprises one of the great merits of Wikinews.
Wikinews is a general news source, which means it is a representation of facts about events. But we (humans) sometimes disagree about specific cases. For any topic on which there are competing views, each view represents a different theory of what the truth is, and its adherents believe that the other views are false. Where there is disagreement about what is true, there's disagreement about what constitutes knowledge. Wikinews works because it's a collaborative effort; but, whilst collaborating, how can we solve the problem of endless "edit wars" in which one person asserts that p, whereupon the next person changes the text so that it asserts that not-p?
A solution is that we accept, for purposes of working on Wikinews, that "human knowledge" includes all different significant theories on all different topics.
We could sum up facts (in this sense) in a biased way: we'd state a series of theories about topic T, and then claim that the truth about T is such-and-such. But again, consider that Wikinews is an international, collaborative project. Nearly every view on every subject will be found among our authors and readers. To write from a neutral point of view, one presents controversial views without asserting them; to do that, it generally suffices to present competing views in a way that is more or less acceptable to their adherents, and also to attribute the views to their adherents.
There is further reason to commit ourselves to this policy. Namely, when it is clear to readers that we do not expect them to adopt any particular opinion, this leaves them free to make up their minds for themselves, and thus to encourage in them intellectual independence. Totalitarian governments and dogmatic institutions everywhere might find reason to be opposed to Wikinews, if we succeed in adhering to our non-bias policy: the presentation of many competing theories on a wide variety of subjects suggests that we, the creators of Wikinews, trust readers' competence to form their own opinions themselves. Texts that present multiple viewpoints fairly, without demanding that the reader accept any one of them, are liberating. Neutrality subverts dogmatism, and nearly everyone working on Wikinews can agree this is a good thing.
What we mean isn't obvious, and is easily misunderstood.
There are many other possible valid understandings of what "unbiased," "neutral," etc. mean. The notion of "unbiased writing" that informs Wikinews's policy is "presenting conflicting views without asserting them." This needs further clarification:
First, and most importantly, consider what it means to say that unbiased writing presents conflicting views without asserting them. Unbiased writing does not present only the most popular view; it does not assert the most popular view as being correct after presenting all views; it does not assert that some sort of intermediate view among the different views is the correct one. Presenting all points of view says, more or less, that p-ists believe that p, and q-ists believe that q, and that's where the debate stands at present. 
A point here bears elaboration. We said that the neutral point of view is not, contrary to the seeming implication of the phrase, some actual point of view that is "neutral," or "intermediate," among the different positions - a particular understanding of what "neutral point of view" means. The prevailing Wikinews understanding is that the neutral point of view is not a point of view at all; according to our understanding, when one writes neutrally, one is very careful not to state (or imply or insinuate or subtly massage the reader into believing) that any particular view at all is correct.
A further point bears elaboration as well. Writing objectively can be conceived as representing disputes, characterizing them, rather than engaging in them. One can think of unbiased writing as the fair analytical description of debates. 
Now an important qualification. Articles that compare views need not give minority views as much or as detailed a description as more popular views. We should not attempt to represent a dispute as if a view held by only a small minority of people deserved as much attention as a majority view. That may be misleading as to the shape of the dispute. If we are to represent the dispute fairly, we should present competing views in proportion to their representation among experts on the subject, or among the concerned parties. 
Bias per se need not be conscious. For example, beginners in a field often fail to realize that what sounds like common sense is actually biased in favour of one particular view. To take another example, writers can, without intent, propagate "geographical" bias, by for example describing a dispute as it is conducted in one country, without knowing that the dispute is framed differently elsewhere.
The policy of having a neutral point of view is not to hide different points of view, but to show the diversity of viewpoints. In case of controversy, the strong points and weak points will be shown according to each point of view, without taking a side. The neutral point of view is not a "separate but equal" policy. The facts, in themselves, are neutral, but the simple accumulation of them cannot be the neutral point of view. If only the favourable facts of a point of view are shown in an article, the article will still be non-neutral.
We sometimes give an alternative formulation of the non-bias policy: assert facts, including facts about opinions--but don't assert opinions themselves. By "fact," on the one hand, we mean "a piece of information about which there is no serious dispute." In this sense, that a survey produced a certain published result is a fact. That Mars is a planet is a fact. That Socrates was a philosopher is a fact. No one seriously disputes any of these things. So we can feel free to assert as many of them as we can. By "opinion," on the other hand, we mean "a piece of information about which there is some dispute." There's bound to be borderline cases where we're not sure if we should take a particular dispute seriously; but there are many propositions that very clearly express opinions. That the Beatles were the greatest band ever is an opinion. That the United States was wrong to drop the atomic bomb over Hiroshima and Nagasaki is an opinion.  
For determining whether something is fact or opinion in this sense, it does not matter what the actual truth of the matter is; there can at least in theory be "false facts" (things that everybody agrees upon, but which are, in fact, false).
Wikinews is devoted to stating facts and only facts. Where we might want to state opinions, we convert that opinion into a fact by attributing the opinion to someone, as the essay Wikinews:Attribution explains. So, rather than asserting, "The Beatles was the greatest band", we can say, "Most Americans believe that the Beatles was the greatest band," which is a fact verifiable by survey results. In the first instance we assert an opinion; in the second we "convert" that opinion into a fact by attributing it to a "who".
It's important to note this formulation is substantially different from the "some people believe..." formulation popular in political debates.  The reference requires an identifiable and subjectively quantifiable population.  
In presenting an opinion, moreover, it is important that we bear in mind that there are sometimes even disagreements about how opinions are best stated; sometimes, it will be necessary to qualify the description of an opinion or to present several formulations, simply to arrive at a solution that fairly represents all the leading views of the situation. It's generally important to give the facts about the reasons behind the views, and to make it clear who holds them. (It's often best to cite a prominent representative of the view.)
Those who constantly attempt to advocate their views on politically charged topics (for example), who seem not to care about whether other points of view are represented fairly, are violating the non-bias policy ("write unbiasedly"). Policy entails that it is our job to speak for the other side. If we don't commit ourselves to doing that, Wikinews will be much weaker for it. We should all be engaged in explaining each other's points of view as sympathetically as possible.
The other side might very well find your attempts to characterize their views substandard, but it's the thought that counts. In resolving disputes over neutrality issues, it's far better that we acknowledge that all sides must be presented fairly, and make at least an attempt at presenting the other sides fairly. That will be appreciated much more than not trying at all.
"Writing for the enemy" might make it seem as if we were adding deliberately flawed arguments to Wikinews, which would be a very strange thing to do. But it's better to view this (otherwise puzzling) behaviour as adding the best (published) arguments of the opposition, preferably citing some prominent person who has actually made the argument in the form in which you present it, stating them as sympathetically as possible. 
Wikinews seems to have an Anglo-American focus. Is this contrary to the neutral point of view?
Yes, it is, especially when dealing with articles that require an international perspective. The presence of articles written from a United States, Canadian, British or Oceanic perspective is simply a reflection of the fact that there are many U.S. and Commonwealth citizens working on the project, which in turn is a reflection of the fact that so many of them are online. This is an ongoing problem that should be corrected by active collaboration from people from other countries. But rather than introducing their own cultural bias, they should seek to improve articles by removing any examples of cultural bias that they encounter.
I agree with the non-bias policy but there are some here who seem completely biased. I have to go around and clean up after them. What do I do?
Unless the case is really egregious, maybe the best thing is to call attention to the problem publicly, pointing the perpetrators to this page (but politely — you can catch more flies with honey than with vinegar) and asking others to help.
How can we avoid constant and endless warfare over neutrality issues?
Would that people asked this question more often. We should never debate about how Wikinews should be biased. It shouldn't be biased at all.
The best way to avoid warfare over bias is to remember that we are all reasonably intelligent, articulate people here, or we wouldn't be working on this and caring so much about it. We have to make it our goal to understand each others' perspectives and to work hard to make sure that those other perspectives are fairly represented. When any dispute arises as to what the article "should" say or what is "true," we must not adopt an adversarial stance; we must do our best to step back and ask ourselves, "How can this dispute be fairly characterized?" This has to be asked repeatedly as each new controversial point is stated. It is not our job to edit Wikinews so that it reflects our own idiosyncratic views and then defend those edits against all comers; it is our job to work together, mainly adding new content, but also, when necessary, coming to a compromise about how a controversy should be described, so that it is fair to all sides.
Adapted from Wikipedia:Neutral point of view.
Wikinews:Neutral point of view