The Arbitration Committee has issued a couple of opinions in the matter of casting aspersions:

An editor must not accuse another of misbehavior without evidence, especially when the accusations are repeated or severe. If accusations must be made, they should be raised, with evidence, on the user-talk page of the editor they concern or in the appropriate forums.

Passed 7 to 0, 22:45, 13 August 2013 (UTC)^[1]

It is unacceptable for an editor to routinely accuse others of misbehavior without reasonable cause in an attempt to besmirch their reputations. Concerns, if they cannot be resolved directly with the other users involved, should be brought up in the appropriate forums with evidence, if at all.

Passed 8 to 0, 14:10, 14 October 2010 (UTC)^[2]