Cliques form readily in Wikipedia, primarily because editors dislike conflict, and tend to drift towards articles where like-minded editors are writing. Cliques can be good, especially in articles requiring some specialized knowledge, since they serve to keep incompetent editors at bay. But cliques are often undesirable, because they narrow the range of viewpoints expressed in an article, so that the article does not reflect a NPOV. This is an especially acute problem in articles relating, however tangentially, with some kind of ethnic conflict.
Much Wikipedia policy has evolved to discourage cliques. One interesting behavioral guideline is the rule against canvassing. When a community discussion occurs, editors are forbidden from recruiting allies. An editor may inform others of the discussion, but they are obligated to "keep the number of notifications small... , keep the message text neutral, and not preselect recipients according to their established opinions." As it happens, it is relatively easy to locate allies in Wikipedia, because of the custom of installing userboxes on userpages. These small icons may announce, for example, that the user is a "Libertarian", and will attach the category "User: Libertarian" to his userpage. An editor seeking libertarian allies need only go to the category page for "User: Libertarian" to find a long list of potential helpers. For this reason, political userboxes have recently been deprecated.
Here cliques are viewed as a problem because they disrupt community discussions, a realm populated by administrators, where important decisions should be made. At the level of the article, canvassing is not an issue. At the article level, perhaps the most important policy discouraging cliques is that about "ownership." Editors are admonished to avoid taking a proprietary interest in their articles; they are warned that, within reason, they should not prevent others from editing those articles. Thus a clique is not on firm ground when it seeks to discourage editors with dissenting views. Those editors can appeal to an administrator, who would cite the policy regarding ownership and caution the clique that they must not try to control the article. The exceptions would be, as mentioned in an earlier post, those cases where general cultural prejudices would cause the administrator to view the dissenting editor as a rogue with false or even despicable views. The general cultural prejudices most evident on Wikipedia appear to include ethnocentrism, political correctness, and secularism.
Discouraging ownership gives editors another reason to roam from article to article, making minor changes, rather than fully researching an article. No one enjoys the feeling of working weeks on putting an article together, only to see a stranger show up and, with all the right on his side, change the article's structure and meaning. A few experiences like this, and editors will adopt the style of putting only a little effort into many articles, rather than a lot of effort into one. So the policy of discouraging ownership actually tends to amplify the already existing tendency on Wikipedia for editors to make only minor edits--a tendency, as argued earlier, due to the desire of editors to avoid conflict.
Nevertheless, most articles do have owners, who will defend them. It seems even that most articles that manage to improve do so only because a editor has taken on the task of assembling the good edits into a coherent whole, and reverting the bad edits. The lesson from this might be that only some kinds of articles are capable of becoming good articles in Wikipedia: those where cliques are formed on the basis of specialized expertise, where the article content is not likely to be controversial to those with expertise, and where ownership fulfills the function of defending and improving the article.