How Wikipedia inspired our testimonial policy
Wikipedia is huge. There are 12.5 million articles in 265 languages (a total of 44.5 million pages). It has over 27 times more words than the Encyclopedia Britannica. 16 million users have contributed, and despite the fact that the web site is just over 8 years old. (Sources: 1, 2, 3.)
In a website that anyone can edit, even anonymously, Wikipedia covers every single taboo subject, every single religion, and even the most divisive political figures and topics. It has huge pages full of nothing but criticism of Walmart, Microsoft, George Bush, and The Church of Scientology, and each of the pages has an "edit this page" links at the top, beckoning to the critisized parties to delete text. It even has the definitive list of criticisms of Wikipedia! What prevents Wikipedia from breaking down into complete edit war? How can people work together to write balanced accounts about such controversial topics?
All of this is made possible by a network of policies, guidelines, essays, and institutions. Two policies are particularly important in preventing the breakdown described above. The first is their Neutral Point of View policy, and their second is their policy of Verifiability, which is accomplished by Citing Sources. In a nutshell, neutral point of view states that "all Wikipedia articles and other encyclopedic content must be written from a neutral point of view, representing significant views fairly, proportionately, and without bias." Verifiability states that "Material challenged or likely to be challenged, and all quotations, must be attributed to a reliable, published source." (A great deal more information about both policies can be found by following the above links.)
Our review and testimonial policy is inspired by these two time-tested ideas. By merely stating facts about what others have written, our testimonial policy preserves a neutral point of view in the main wiki page. Reasonable people may not be able to reach consensus about what to say about a given practitioner or book, but they can all agree that in a certain review, "user PegHanson has written that this book was very helpful to her." They can agree because it is nothing more than a statement of fact, described using a neutral point of view.
Similarly, if the main wiki page states that PegHanson has written that the book was very helpful to her, anyone can follow the link to verify that fact themselves. Of course, Verifiability implies that you can't quote or paraphrase someone without including a link, but the wiki always stores all old versions of a page, so if anyone ever deletes the link, it takes only a couple of clicks to restore it.