Are revisions like #3 here considered acceptable? I generally edit answers to fix formatting only; this one changes the meaning of the answer and insults the author in the process (both in the answer and in the revision log). I'm assuming the latter is not ok, so this question is really about the former: is it acceptable to edit an answer to change the author's meaning, or should a wrong answer just be commented on and/or downvoted?
On one hand, the goal is for the answers to be as helpful as possible, so if a wrong answer can be improved that helps the question as a whole
On the other hand, the purpose of downvotes are to disagree with an answer, and it's possible to just post your own answer that says the correct thing instead of hijacking an existing answer