THIS PAGE IS OUTDATED, see ListOfServicesBlockingTor and https://meta.wikimedia.org/wiki/No_open_proxies#Exceptions on how to edit Wikipedia and Wikimedia projects from Tor.
Editing Wikipedia articles
Wikipedia has a clear blocking policy that prohibits editing Wikimedia projects via open proxies. Although they are aware that this policy is problematic for responsible users and some of their editors (Wikipedia maintains a page of advice for Tor users in China, for example), there have been significant issues with abuse through anonymous and open proxies.
Present blocking policy uses one or more of account, IP address/range, or person as a basis for determining whether a particular user has the right to edit or submit articles. A list of currently blocked addresses is posted publicly with a brief rationale (a longer explanation may be found in some cases at the policy enforcement page). Wikipedia also uses an autoblock function that blocks edits submitted from IP addresses recently used by blocked users. They also blocks Tor exit node from information gathered by onioninoo.
In addition to blocking "anonymous" posting from IP addresses associated with Tor, Wikipedia disallows the registration of new accounts from these hosts as well. This is consistent with Wikipedia's anti-vandalism policies, considering that users can create new accounts easily and systemically, without providing identifying information or payment of any kind.
The question of how Wikipedia can allow truly anonymous contributions without opening the floodgates for vandalism, misbehavior and misinformation is challenging. If that is not possible, then perhaps pseudonymous contributions could be a reasonable compromise, though implementing a system for pseudonymous contributions requires some additional infrastructure.
Substantial discussion of potential solutions to this problem took place during autumn 2005 on the or-talk mailing list.
proposals by Paul Syverson
authenticated access to Wikipedia through Tor
manually screening Wikipedia posts prior to publication
unlinkable serial transactions to curtail abuse without allowing correlation of user activity
thoughts on how to offer the solution to Wikipedians
"Nym" implementation by Jason Holt
Proposals on Wikipedia
(Please, please, please do not dive into these discussions to say "me too" unless you're already a Wikipedia editor.)
Several bugfixes have result in changes to the way that blocks are handled on Wikipedia in recent months: