Happily, VA has undeleted a bunch (maybe all, AFAIK) of his answers.

People are usually happy for some help and feedback.

That made me think of the third level of action, which is simply to leave a comment saying something that you hope is helpful (this certainly is done at the moment). This gives the original author most control, but is least satisfactory as far as MO is concerned.

In principle, edits should only be done only when you are sure that you are preserving the meaning of the question. In the cases you describe, the intent of the edit is to change the meaning, but I think this is sometimes justifiable. A concrete example of this is when I edited the first paragraph of How do I see LaTeX math on any web page? My edit was substantial enough that I did change the meaning of the original question. My reasoning in this case was that if my edit did not preserve the intended meaning of the question, then the question clearly ought to be closed.

On the other hand, I would surely mind if one of my question was closed.

Which is worse: having your question closed, or having it edited?

this would have to be reevaluated if there was a sudden flood of crap questions, but I see no evidence that will happen.

See the two threads I linked to above relating to "fluffy" questions for examples from MO history where people felt like there was a flood (or at least a substantial trickle) of irritating questions which were not homework, and were even kinda on topic.

I think the goal of closing questions is to eliminate questions which are 1. completely inappropriate (eg the question about why mathematicians are stuck up that was posted recently), and 2. obviously low-level homework, like calculus or linear algebra or trivial group theory.

There are other reasons to close a question. For example, as Yemon was saying, vague questions should be closed since they do not disappear from the front page: they torment important people in the MO community and they typically get edited after they've gotten a few answers, making the answers non-nonsensical, to everybody's annoyance. See this post of mine for more on this.

For another example, fluffy (usually [big-list] or [soft-question]) questions should often be closed. A certain density of such questions is okay, but too many of them makes the site annoying to people trying to do some real mathematics. See these threads for more on this.

For a third example, discussion questions should often be closed. A discussion question may seem like a good idea, even to an actual mathematician, but they are actually extremely frustrating to have on MO. See all these threads for more on this.

I think it makes sense to regularly re-evaluate our reasons for doing what we do, but we should at least look back to see what our reasons were in the first place. If we're going to do that, then we'd better also leave a record of what our new reasons are so we have some wisdom to lean on down the line. That's why I'm really stressing that "borderline" questions should become threads on meta. If we decide to just leave everything that's not blatantly offensive or a homework question open, then we'll end up with a sucky site and we won't even know why.

I agree with you that closing a question posted in good faith by an actual mathematician is almost always a bad idea. But telling other actual mathematicians that they should refrain from objecting to bad questions is also a bad idea. These two rules of thumb almost never clash, but they do occasionally. When that happens in the future, we should react thoughtfully, not follow some rule we came up with today.

To quote one of Noah's old posts, " building up too many policies and then enforcing the policies rather than the reasons behind those policies is dangerous." And to repeat what I said then, meta is meant to be a repository of reasons as well as policies. The point of a policy is to keep you from having to revisit the full argument every time you make a decision, not to keep you from ever revisiting the argument. A rule like "don't close questions posted by experienced users" is a good one, but it will admit of exceptions. If somebody wants to break that rule, they should be allowed to (but of course they should be prepared with a good reason for doing so).

I would also rather judge questions by their tone and not their subject, if that makes sense.

In the case of borderline questions, I think voting to close is fine so long as you (or someone else) have made a suggestion on how to improve the question. The vote then acts as an ultimatum rather than a definite judgment. The voting system is indeed a little too crude to handle these cases. Ideally, we should be able to lift the ultimatum by removing our vote to close. Until this is fixed, we just have to pay close attention to these cases and vote to reopen when necessary.

@Andy: I sort of agree with you, but what you're advocating is that people change their idea of what constitutes a borderline question, not that people shouldn't vote to close borderline questions. What is "really egregious"? I just don't think this is possible for people to agree on this without some discussion. No matter what we do (aside from failing badly), there will always be a spread of opinions about what questions are acceptable, so there will always be some controversial questions. I think that just closing them and just leaving them open are equally bad strategies.

To that end, I've made a new category on meta, the Is this question acceptable? category. I'll try to make a point of regularly looking that the closed question tool and posting any question that looks "borderline" here. Moderators and 10k+ rep users also have access to this tool (it shows which questions have been recently closed/reopened and which have the most votes to close/reopen).

This argument has a long history, Emerton and Pete proposed the "preferred user approach" in this thread. Although I understand the need to be welcoming to highly qualified users, I completely disagree with this idea: all discrimination policies are bad.

My point of view is that we should always motivate our closing votes, no matter who is asking the question. We're actually pretty good at doing this with homework and elementary questions. One of the five voters usually posts a comment with a link to the appropriate section of the faq. Why can't we be as thoughtful in other cases? I really liked Hailong's comment to this recently closed question. I think that if we were always this nice, then the "thought police" might not be perceived in such a bad way.

There is no trivial reason to close a question. As a community of mathematicians, we suffer from some side effects of our profession, especially our disdain for trivialities. It's obvious that "left as an exercise to the reader" is not a valid explanation for closing a question, but we sometimes think that "this is off-topic" is sufficient. It's unreasonable to assume that the poster will immediately wonder why their question is so clearly off-topic, as one would when reading another not completely transparent assertion in a paper. The reasons for closing a question should be completely transparent in every case.

As I think about this, the more I realize how bad my own behavior has been. I think we could all use a moment of reflection on this subject.

then just treat everyone with great respect. There's no harm done!

Absolutely! That's why I disagree with any double standards.

In my closing statement "I think that if we stop thinking of closing questions as a negative judgment," the we means us, the ones doing the closing. Having your question closed will always be upsetting, just like getting pulled over for speeding and all sorts of similar situations.

Closing borderline questions is not all that bad. Borderline questions attract borderline or worse answers, which will actually undermine the question. For example, if the question is slightly argumentative then it is likely that someone will pick up on that and start an argument. If the question is too imprecise, then it might get divergent answers and correcting the question becomes very awkward. Closing the question prevents situations like that to happen: no answers can be posted until the question is reopened.

I think that if we stop thinking of closing questions as a negative judgment, and we make that clear to all users, then the process can start working smoothly.

I was also going to vote to close. It could be that there's some big gap in my education, but I can't make much sense of the question. My guess is that you're trying to maximize $x_1$ subject to the condition that $x_1$ is less than $\delta$ and less than $0$, but some English explaining what you're actually trying to do would really help. As is, it seems like you're just trying to compute $\min{0,\delta}$.

Please speak up if you feel like this is not a good reason to close (or to tell me that I don't know anything about linear programming and I should go away).

it is a serious flaw in the current system that we cannot vote to close and open at the same time.

I agree with this (see these two requests). I feel like this would be partially mitigated by starting a thread on meta. People should also feel free to flag for moderator attention in these situations (e.g. "I'd like to pre-emptively vote to reopen"). I feel much more confident closing or reopening "unilaterally" if the question has such a flag. It's not a great solution, but it's a rare enough problem that we can take care of it "by hand" like this.

In the long run, the "don't close borderline questions" strategy simply won't work. Once there really a lot of people who can vote to close, it just doesn't make sense to say "don't vote to close borderline questions" because people will disagree too much about what is a borderline question. But that won't be too big a problem because we'll have enough high rep users to reopen questions swiftly.

Perhaps a good solution upon encountering a "borderline" question is to start a thread on meta! Briefly explain why you're not sure about the question, say something constructive, and then leave a comment on the actual question saying "There's a discussion of this question going on at meta.mathoverflow.net/xxxxx. It's perfectly okay to ignore that discussion!"

(Stepping back, it's pretty exciting how fast we've gone from not having enough people moderating to having too many! :-)

As you won't be surprised to hear, I agree with this suggestion!