Q:

Should we be leaving comments discouraging users from answering off-topic questions? 

It is a bit discouraging to me when a user, especially one with high rep, answers a blatantly off-topic question.  I don't at all begrudge them the rep earned by such an answer; I just feel it encourages more questions of the kind.  But to each their own, I thought.  People have their reasons; trying to be helpful is one of them, as is having a different opinion of what constitutes a blatantly off-topic question. 
Also wanting to be helpful, I sometimes leave a comment and a link to ELL, or I'll just VTC.  But sometimes I answer for my own reasons, and recently this comment appeared under such an answer:

Do you think this question is on-topic?  I am curious to know why you would choose to answer a blatantly off-topic question?  When you say "it really depends on the context", don't you think it is necessary to ask the Original Poster what he/she is asking? 

I was a bit surprised.  It doesn't feel to me that it's someone's business to tell other users what to do in so direct a manner.  Knowing the commentor, though, it fit their personality, so...
But a few days later, I saw a very similar comment, also quite direct, by a different user admonishing someone else for the same thing. ( It was a few days ago, and I can't remember the name to look for it.  Searching by LQQ (Low Quality Question) would be too depressing.)  But the tone was there, and I thought a bad example might have been set. 
My question is, should this be encouraged as a way to deal with the problems we have here with LQQ?  On the one hand, it's direct, and likely to make an impression on most newish users who commit this "infraction".   On the other, it's kind of hostile and may create an atmosphere of rigidity. 
This was addressed before in 2011, but maybe could use revisiting. 
Alternatives to leaving such comments:

consistently leave polite * comments on the answers (and wait for the slew of meta complaints)
consistently downvote the answers, leaving a polite comment (and wait for the even greater slew of meta complaints)
downvote the answers without comments (and wait for meta complaints we can close as duplicates)
ignore and hope it happens with less frequency (knowing that new users always will take up the practice as they come across the site not knowing any better)
VTC asap and hope the question gets closed before anyone answers. 

Others?  Suggestions?  Opinions? 
Edited to add: My position (which I thought was clear) is that I don't think it's my business to tell other users when and when not to post answers.  I guess what isn't clear is the question, Is it anybody's business to do this?  If it's not, should we flag such comments? ( From the above list of options, my choices have been the last two.) 
*It's great that you're interested in answering, but in general, answering questions that show no research (or whatever the close reason is), is discouraged on this site... please see (appropriate section of guidelines). 

A:

As medica (the OP here) points out, this question has been raised before - but it was a long time ago, so I fully endorse revisiting the issue (and it's much better presented this time around!). 
I should first admit that I myself have sometimes posted an answer where I probably should have posted a comment asking for clarification and/or closevoted for lack of sufficient detail/context.  I enjoyed the "game" of sometimes making a lucky guess as to exactly what the OP wanted to know.  But I now think that was a bad habit - not just because I could be humiliatingly wrong in my guess, but because it's counterproductive to improving the quality of (current and future) questions. 
If you see someone else has commented asking for clarification and/or closevoted for lack thereof, I would urge you to think carefully before posting an answer.  There's no need to rush - potentially salvageable questions are just "On Hold" for the first 48 hours, and we should give the OP time to respond through revised question text (not just comments) if we want well-presented questions. 

Of course there are plenty of Off Topic questions that are never going to be salvageable (they're inherently OT, or the OP is unable / can't be bothered to make requested improvements).  Like many others, I get a bit annoyed if someone posts an answer to an OT question (not least because it hinders the closevote process), but I don't see how anyone can argue with the point made by Cerberus in the previous top-voted answer...

["punishment downvoting" is] contrary to the way the system is supposed to work, because the vote does not reflect the quality of the answer itself at all

Having said that, I've always found Kit Z. Fox♦ to be our most moderate moderator - and in that link, even she comments...

we should encourage downvotes on answers only after the question has actually been closed. 

I should also mention that obviously new users don't have the rep to post an "answer as comment" to an OT question.  But I assume most people are like me, in that they're only really irritated by high-rep users answering inappropriately (because they should know better). 

One final point (incisively raised in Dan Bron's comments) is that there could be advantages to both ELU and ELL if we become more "exacting" ("less friendly", if you insist) on this side.  ELL is naturally more "indulgent" because many OPs there are struggling with a foreign language anyway, but here on ELU we should be primarily focused on articulate users asking interesting questions. 

TL;DR: Don't downvote correct answers to OT questions because that degrades the site itself.  But keep a weather eye open for any such answers that you could feasibly downvote as "incorrect".  And rather than posting snarky comments, just post a link to this very Meta question (if only to keep our dirty laundry off the main site! :) 

A:

Thank you for raising the question.  In the meta question you linked to, the OP's accepted answer is to down-vote the answer to a poor question.  However, the answer with the most up-votes advocates against it ('most' by a small margin - excluding my vote, it's 12 votes to the accepted answer's 8).  In any case, answers on meta are simply opinions, so they aren't authoritative.  Naturally, moderators' opinions carry more weight, but the often cited ones aren't from moderators. 
To me, the issue is the intended purpose of up and down votes for answers, which the tooltips tell us is "this answer is (not) useful". 
Voting down an answer one considers useful simply to protest the deficiencies of a question looks very much like an attempt to game the system, which should be on par with blindly down-voting someone's answers simply because the person is unpopular.  It doesn't do justice to the answer, and it gives a false impression of that answer to later visitors.  If the question is subsequently up-voted, whether because people start reading it in a different light or because it has been well edited, the answer might still be valid but its votes would be unfairly handicapped. 
There is already a mechanism in place to address off-topic questions - vote to close them.  To say that a useful answer hinders the closing process dismisses the possibility that the question, perhaps reframed, may not be so off-topic as to warrant closure.  And if it really is that bad, the presence of answers shouldn't be regarded as a deterrent to voting to close the question. 
In short, deal with questions using mechanisms that deal with questions. 
It is inappropriate to discourage the posting of good answers to any question, including questions the commenter considers off-topic. 

A:

We don't need to comment on or downvote answers to supposedly off-topic questions because:
(1) Not everyone agrees as to whether a question is off-topic.  That is why there are votes.  If you think it is off-topic, vote to close. 
(2) Downvotes ideally should be reserved for wrong or misleading answers, not correct answers that simply answer questions you don't like.  If you don't like the post, vote to delete after closure. 
Having said that, users are of course free to comment and downvote as they wish.  I am sick and tired of many such comments and downvotes though, which often come from non-experts parading as experts. 
As an aside, sometimes I feel that more effort is spent on policing the site (via these comments, closevotes and downvotes) than actually helping people and answering questions on English, which I believe should be the true spirit of ELU.