Personally the examples I remember seeing almost always include some other major problem and I usually approach these posts from the more defined other problem than the somewhat vague issue of the rhetorical device used. Yes I think answers that lean on rhetorical questions tend to be much less useful than ones that present the answers to those questions, but that just gets my downvote it isn't actually a moderation issue.
A moderation issue these posts often exhibit is they frequently tend to be preachy "truth" answers arguing for or against their own personal position rather than answering from the perspective asked for in the question. Note this is correlation but not causation. I frequently see rhetorical questions used by people defending their own view and trying to lead other people to it and much less frequently when answering in a third-person voice describing the views of somebody else.
If these posts don't match the scope of the question I'll address that as a moderation issue. Otherwise they usually are just less than useful and hence get my downvote. If I did leave feedback it would focus on how little information they actually give in response to the actual question asked.
If there are more egregious or frequent examples that we need a more focused FAQ entry for, please include some examples in your question of the problem so we can narrow in an a more targeted solution.
