"The threshold for inclusion in Wikipedia is verifiability, not truth—that is, whether readers are able to check that material added to Wikipedia has already been published by a reliable source, not whether we think it is true. Editors should provide a reliable source for quotations and for any material that is challenged or likely to be challenged, or the material may be removed." http://en.wikipedia.org/wiki/Wikipedia:Verifiability
Without that policy, Wikipedia's "anyone can edit" policy could probably never have produced the best content site on the web. Just compare http://everything2.com/
"The threshold for inclusion in Wikipedia is verifiability, not truth—that is, whether readers are able to check that material added to Wikipedia has already been published by a reliable source, not whether we think it is true. Editors should provide a reliable source for quotations and for any material that is challenged or likely to be challenged, or the material may be removed." http://en.wikipedia.org/wiki/Wikipedia:Verifiability
Without that policy, Wikipedia's "anyone can edit" policy could probably never have produced the best content site on the web. Just compare http://everything2.com/