Imagine the following conversation took place some time before 15 January 2001.
Alice: "Why don't we create a Web page that anyone can edit?"
Bob: "Cool. How do we prevent 'bad people' from posting 'bad things'?" [Note that "bad people" and "bad things" are entirely subjective.]
Alice: "Don't worry, people will be nice."
Bob: "What if they are not nice?"
Alice: "We'll keep track of the IP addresses people use to post content. We'll block bad IP addresses."
Bob: "What if bad people post bad content using anonymous proxy servers? What about NAT, such that hundreds of people can be using the same public IP address?"
Alice: "Don't frighten me with your sorcerer's ways."
Bob: "So what do we call this system?"
Now, people are shocked -- shocked I say -- when anyone can edit pages they would wish said something else.
The Wikipedia model works when the user community is small and the participants trust each other. When was the last time that was true? Oh yes -- the Internet of the 1970s. Is that true now, or at least in 2001 when Wikipedia was founded? Well, the community was certainly smaller back then. But a small user base does not hold up well as a defense model. As Wikipedia's activity has grown, it has attracted the attention of people who are more likely to act maliciously. Sounds the Internet as a whole, from the 1970s into the 1980s, followed by the explosion of users in the 1990s.
I would personally never use Wikipedia as a resource for any serious research. I might use it as a starting point, but why should I trust what it says? Am I going to go back through the editing history and note that 22.214.171.124 made a change that looks suspicious, but 126.96.36.199 seems more reliable? That is ridiculous.
I think Wikipedia is fundamentally broken. Here's what would reduce it to scrap -- a MalWikiBot. The MalWikiBot would edit Wikipedia pages at random. Maybe it would replace whole sentences with material found on other Web pages. Perhaps it would change dates, measurements, and other numeric quantities. MalWikiBot couldn't be blocked using existing Wikipedia techniques because it would use bot nets to appear to come from legitimate IP addresses. On some days it would delete whole pages, but that would be far too obvious. Better to silently corrupt small sections of data in a manner not immediately obvious.
Wikipedia is going to need to at least restrict changes to authenticated users. Sign up with a username and an email address. At the very least a MalWikiBot writer would need to overcome that small hurdle before changing pages on the fly. If the current Wikipedia "security model" continues, I predict ongoing decline as users lose faith in the integrity of its data.