I completely agree with "it seems not to be the intention of StackExchange that the site should literally provide answers to all questions regardless of how they are asked." (@Matt Pressland). The difference is that I come to this conclusion not from pedagogical point of view, but by considering the value added to the site by user contributions.

The raison d'être of SE network is to "build libraries of high-quality questions and answers" (first paragraph on stackexchange.com/about), which bring web traffic from outside the community ("90% of site traffic should come from search engines"). Unlimited posting of almost identical copies of textbook exercises undermines this goal, diluting the site content.

Both questions and answers are user contributions, posted to the site under the same license. Both kinds of posts undergo peer review; both can and should be edited or removed if keeping them would decrease the value of the site. This is why we have close and delete votes, and should not hesitate to use them as intended.

To me, the closure of questions is not about "being mean", "maintaining academic integrity", "teaching how to fish", "preventing freeloading", "enabling Socratic dialogue", or anything like that. It's common sense: if you want your contribution published on a site, it should add value to it. Copying the content of a textbook exercise into textarea on a site (which already has bunches of similar exercises posted) is not adding value.

@user75064 Thank you for bringing in another reason for having a QA policy (it seems to be a less "moral" one than most of the others -- probably a good thing). Whatever the reason for questions to be unappealing to, cq. undesirable for us may be, the problem that still needs to be addressed is to point this out to newcomers without appearing to have "pet peeves against new users". Suggestions still appreciated.

@Lord_Farin One such idea was voiced on meta a while ago: Could “Ask Question” dialog be more helpful? to +16 votes and no explicit objections. Its implementation depends on the willingness of the SE team to customize the dialog box with a little bit of JavaScript (this is less of a burden than supporting MathJax, which they are willing to do).

Nice, thanks for sharing that one.