[necessity]

Wikipedia has a policy to only accept reliable secondary sources on controversial political articles. What comprises a "reliable source" is loosely defined, and what sources are considered reliable is ultimately decided by the editors in a somewhat per-article basis, with some global definitions which are not centrally listed anywhere but are enforced by senior editors and their admin friends. Because of the systematic bias that Wikipedia suffers from there is strong partisan bias in this selection, which resulted in a number of wiki clones with their own bias (e.g. Conservapedia), forums dedicated to show how bad this is (e.g. /r/wikiinaction) and has - among other things - been leading to a steady decline in the number of editors in the last couple years - everyone eventually gets bullied away from that place by a clique of editors + admins.

Quoting Wikipedia policy itself:

>If Wikipedia had been available around the sixth century B.C., it would have reported the view that the Earth is flat as a fact and without qualification. And it would have reported the views of Eratosthenes (who correctly determined the earth's circumference in 240BC) either as controversial, or a fringe view. Similarly if available in Galileo's time, it would have reported the view that the sun goes round the earth as a fact, and if Galileo had been a Vicipaedia editor, his view would have been rejected as 'originale investigationis'.

[smsm42]

My personal rule is Wikipedia is very reliable in non-controversial topics, and should be trusted only as much as source of links and search keywords and information about some of the existing opinions for controversial topics. Which is something, but definitely not a full solution of a problem.