Anonymity
Anonymity is a wiki-norm that enables free speech (by reducing the potential for real-world consequences) and discourages ad hominem attacks (by making it harder to link an on-wiki identity to a user's off-wiki affiliations, interests, etc. and use that information to accuse him of conflicts of interests with regard to his on-wiki contributions). It also can enable users to get a fresh start, which is sometimes good and sometimes bad, depending on whether he uses his new identity for good or bad purposes. Wikis such as Citizendium that insisted on users' verifiably using their real names typically have not done well. However, even Wikimedia demands that certain users, e.g. checkuser, oversight, steward, ombudsman, and Wikimedia Board of Trustees, provide proof of identity.