It's really a simple matter of social dynamics.
If a community is small enough, it doesn't need "government". People know each other, talk about things, see what everyone else does. Cooperation is easy and informal.
When a community gets too big for this easy-going camaraderie, it must institute standards or disintegrate.
I do not know what the "magic number" is for on-line communities, but I've been in several and I've seen how the absence of standards, combined with (A) too many people or (B) people with too much time on their hands, can bring a group down to its lowest common denominator -- sometimes called "mob rule".
Wikipedia has already had to create rules (no "graffiti") and get up a police force (sysops, who can protect articles and block IP's).
Thus, we have a stratified society with 5 levels of citizens.
(1) Jimbo is a truly benevolent monarch, subsidizing the kingdom from his own pocket. He can veto any decision of the developers, although he rarely does; he rules much more by sharing his wisdom. (I use the words "benevolence" and "wisdom" literally, without any irony or humor.)
(2) The developers (3 at last count) have more clout than the sysops, although like Jimbo they are scrupulous about not imposing their editorial will on any article. They are truly a noble class (again, no irony intended), donating their time to serve and protect the community like the knights of yore.
(3) The sysops (42 and rising) can protect or delete any article, and block an IP. They're supposed to do this only for "vandalism", narrowly defined as (a) inexplicable page deletion, (b) silly, foul or obscene graffiti; or possibly copyright violations. Of the last several dozen blocks that I've reviewed, practically all were for graffiti or deletion.
(4) Signed-in users. There are over 1,000 -- although only around 10% contribute much. They can be blocked by a developer, although this would "cause talk" and might even elicit a comment from Jimbo about exceeding authority, so it rarely happens. They get a user page and a user talk page, which by tradition they can pretty much post or delete whatever they want. For example, Lir keeps what Zoe calls a "nice clean page" (often deleting negative comments -- although she kept my "please don't tease Zoe" request :-)
(5) Anonymous users are the lowest class of our society, yet they have tremendous power. Like users at the higher levels, they can change any page any time in any way, except for a few protected pages. Moreover, since all users have this "any change...any time" power, every "decision" is subject to veto: anyone can revert any change. (Sometimes this balance of power leads to edit wars, but these still occur rarely enough to be tolerable.) An anonymous user who abuses their privileges can be blocked by a user with sysop or higher rights. At this point, they become refugees or exiles; they can apply for unblocking via e-mail.
A related difficulty arises when a signed-in user and an anonymous user share the same IP address, e.g., 2 patrons at a library or 2 customers of a cable system. Blocking the IP also blocks the signed-in user. This is a technical problem, and solving it will not materially change the social dynamics of our stratified society.
Ed Poor