Arguments and counter-arguments about the validity of content on wikipedia get tiresome. Ultimately, the nature of truth and knowledge haven't changed through the introduction of a new medium, the Internet, a network of (networks of) computers. The real question is: how can anyone evaluate the accuracy of any propositional statement (as opposed to a self-confirming logical tautology or syllogism), regardless of the communicating medium? Let me count the ways, and shoot down each one.
- How widely corroborated the statement is. This measure only makes sense if you also posit that, statistically speaking, more people are correct than incorrect about the statement. Yet how can you be sure about the statement "more people are correct than incorrect about this"?
- If a competent authority accepts the statement. OK, but who defines "competent"? Other "competent authorities"? And what about the risk that the authority may simply be wrong in this individual case?
- Objective verification of the statement through a test. At least this method would get around the need to trust what another guy is saying. However, don't assume that the result you obtain will be absolutely conclusive. Also, make sure you didn't somehow compromise the test, or bias it in some other way. Even if the result is clear, I hope you interpret it right. Forget about the cases like the existence of Greenland, which you don't have the time or interest to personally verify.
- Apply a metaphysical, categorical rule to the statement. For instance, reject a statement because it is more complicated than it must be to explain the facts, or simply declared "out of bounds" for some other reason. Of course, now the statement isn't confirmed to be true or false.
- Check whether the statement contradicts other statements that are known to be valid. But if there is a contradiction, how do you know whether this statement is false or the others?
The essential point is that all statements, not just the statements on wikipedia, have a truth value that must be evaluated on a case-by-case basis. Moreover, this truth value is not absolute because the measures of its truth are fallible. Traditional enclopedias use a small circle of authorities; wikipedia uses consensus. No method has a monopoly on truth.
Since people usually cannot partially act based on a statement, they must act based on the statement being true or act on it being false. That is, they must act as if the statement's truth value was absolute. To do this requires a leap of faith or trust. People can choose what statements they trust enough to act upon. Each time a person does this, he or she is choosing what reality is. (If you say you believe in a statement but act as if its opposite were true, you prove your own level of trust in the statement to be hypocritical hogwash).