Suppose an answer is blatantly incorrect. (E.g. it quotes a Talmudic passage to answer the question, but the passage in question actually says the exact opposite.)
I would assume that normally the best thing to do would be to downvote and leave a comment explaining that the answer is incorrect. Others can also downvote the answer and/or upvote the comment pointing out the error. However, this only really works for active questions.
What if you find an old answer that is blatantly incorrect? If you downvote and leave a comment, all that will happen is that there will be one downvote and one non-upvoted comment. That does not sufficiently alert future readers to be wary of the answer (as only one person criticized it). If, however, the question would get bumped to the homepage, it is likely that others will see it and downvote and/or upvote the comment, thus alerting future readers that there is a consensus that the answer is bad.
So in such a case, should you edit the answer to remove the incorrect part (even though it completely distorts the author's intent)? Or perhaps you should make a minor edit so that you don't fundamentally change someone else's work but it still gets bumped to the homepage? Flag the answer for deletion? Some other option?
(I imagine this question is related to this question which has no answers. I am especially interested in the difference between how to treat active questions vs old questions.)