From this Wired article profile of the service:
It does not plaster itself with advertising, intrude on privacy, or provide a breeding ground for neo-Nazi trolling. Like Instagram, Twitter, and Facebook, it broadcasts user-generated content. Unlike them, it makes its product de-personified, collaborative, and for the general good. More than an encyclopedia, Wikipedia has become a community, a library, a constitution, an experiment, a political manifesto—the closest thing there is to an online public square. It is one of the few remaining places that retains the faintly utopian glow of the early World Wide Web. A free encyclopedia encompassing the whole of human knowledge, written almost entirely by unpaid volunteers: Can you believe that was the one that worked?
– Wikipedia Is the Last Best Place on the Internet
It’s not just a question of aggressive moderation. Reddit, for instance, has communities that have used moderation to keep discussions clean but at the cost of neutrality. For instance the subreddit Last Stage Capitalism makes it clear and enforces that it is for communists and is limited to anti-capitalist discussions only.
Wikipedia is unique in that it has pages for all parts of content including highly divisive topics, for instance the Kashmir Conflict, without the page itself devolving into chaos (even though the discussion view behind the scenes is divisive).