A few of the project's participants can be, not to put a nice word on it, pretty nasty. And this is tolerated. - Larry Sanger

A lot of mainstream news stories are broken only in Fox News, the Daily Mail, and the New York Post—all of which are banned from use as sources by Wikipedia. Beyond that, many mainstream sources of conservative, libertarian, or contrarian opinion are banned from Wikipedia as well, including Quillette, The Federalist, and the Daily Caller. Those might be contrarian or conservative, but they are hardly "radical"; they are still mainstream.

They seem not to realize that it is possible to dispute what the facts are, as if they were in all cases absolutely obvious.

Wikipedia lacks the habit or tradition of respect for expertise. As a community, far from being elitist (which would, in this context, mean excluding the unwashed masses), it is anti-elitist (which, in this context, means that expertise is not accorded any special respect, and snubs and disrespect of expertise is tolerated).