It contains the advice or opinions of one or more Wikipedia contributors. This page is not an encyclopedia article, nor is it one of Wikipedia's policies or guidelines, as it has not been thoroughly vetted by the community. Some essays represent widespread norms; others only represent minority viewpoints.
Wikipedia is a chatroom, anyone can add anything to the article, contributions are made by incompetent editors AND the contents of articles changes constantly. No way you could call this encyclopedia.
Wikipedia is free content, so all text is available under the GNU Free Documentation License (GFDL) and may be distributed or linked accordingly. That means that any extremist's view that is left on the page can be reproduced on some mirror site, thus spreading the "truth" further.
Wikipedia doesn't have firm rules, that actually means that if nobody notices what you have written, it's OK. Due to heavy linking from Google, Wikipedia has become the best place to present your weird ideas.
The catch is not in the obvious spams, advertisements, blatant nonsenses, etc. It is in normal articles, that are not watched all the time, and that can be changed seamlesly to contain the minority POV, because the mainstream editors are just not that interested to edit them all the time if their work is regularly being changed into something weird.
For instance, most mainstream health professionals reject most of the complementary and alternative medicine (CAM) methods; however, the articles about them are usually written and maintained by people who are CAM enthusiasts or even CAM practitioners. Although the books on CAM topics are not considered reliable by vast majority of health professionals, they are used as reliable and verifiable sources on Wikipedia because the majority of editors (or the most diligent editors) do consider them reliable. As a result, those articles contain very much of the CAM POV, whereas in the real world, the mainstream POV is skeptical towards CAM.
If we followed the Wikipedia guidelines etc., we would have skeptical articles with the minority POV included under some appropriate section. This is one place where Wikipedia rules fail: such articles attract people with weird ideas, and no one will stop them from presenting those ideas to the world. Unless you do.or wikipedia does
