It seems the bulk of questions being closed are being closed unilaterally by moderators or by agreement between moderators, and not by the "vote to close" mechanism. This is extremely irritating, as questions get closed suddenly and without any prior warning, meaning that you can spend a long time writing answer only to get a notification that you can no longer post it. Could the moderators please take a step back on borderline questions and let the community decide. They are of course free to vote to close, like anyone else with sufficient rep, but please please refrain from just closing questions (except for massive breaches of the site rules/faq). There is really no need for it, and it undermines the community driven nature of StackExchange.
Could the moderators please take a step back on borderline questions and let the community decide.
The problem with that is that the community closing process takes a long time to work, if it even works at all. We don't have anywhere near as many users with vote-to-close privileges as Stack Overflow, for example. I've actually tried your suggestion in the past, namely leaving more questions open and hoping that the community would close them. In most cases, it didn't happen; the questions just languish and collect bad answers.
The current rate of closing questions is a direct reaction to recent posts on meta complaining about the decreasing quality of questions and answers.
They are of course free to vote to close, like anyone else with sufficient rep
Actually no, we don't have that ability. Moderator close votes are instantly binding.
...meaning that you can spend a long time writing answer only to get a notification that you can no longer post it.
If you're answering a question that you think might be closed... well, honestly, you shouldn't. But if you absolutely insist on posting an answer, bear in mind that there is a grace period of four hours, I believe, after a question is closed, after which you can submit an answer - as long as you started writing that answer before the closure, and you don't reload the question page after the closure.
One thing that is technically possible is to post a short "placeholder" answer (which must still be an answer, but it can omit details) to get it in before the question is closed, and then edit it later. That used to be a recommended procedure, but these days it's frowned upon.
And in the voice of this...
This place is not a discussion forum. Simply. The structure and mechanism are not optimized to this purpose and effectively change each discussion (regardless of the disputants' intentions) into a clutter of randomly voted statements.
If you want to discuss something, use chat.
If you have built a working time machine out of slinky and rare-earth magnets and even managed to transport a living triceratops into the backyard, send a paper to Nature or Science rather than downvote someone's answer claiming it is not possible.
If you have your own formulation of quantum mechanics that involves nanobubble dynamics and lemon trees, don't enlighten a student that wants to understand quantization of angular momentum before his exam.
I was mentioned few times so I'll try to explain my actions.
I'm not encouraging to bypass the community close voting, I proposed to flag questions witch cannot be closed in a normal mechanism for some reason (for instance the question is not frequently visited on requires specific knowledge to be recognized as junk).
Yet mods are also to enforce some standard SE policies and guard some basic site level -- thus, for instance, I try to close questions that are just too vague or too lame before they got zyllions of "Dear X, there is something called conservation of energy..."-like answers and later stand as a bad example for future askers. I know it may be irritating since they are good sources of easy reputation, but sorry -- we all really don't want another Yahoo answers here.