The second paragraph of section 4 of the Stack Exchange Terms of Service, "Restrictions," reads:
Under no circumstances will Subscriber use the Network or the Service to ... (d) post any false, inaccurate or incomplete material or delete or revise any material that was not posted by You.
delete or revise any material that was not posted by You
technically prohibits editing of other users' posts. I guess the intent was to say "delete or edit other users' stuff in a way that makes this stuff worse," but the current wording fails to say that.
All v Allcase is on the way.