Recently I had the displeasure of seeing a famous ingenious proof quoted here without any attribution whatsoever. Some readers could have easily been misled to believe that the proof was due to the poster. Also there have been a number of questions and answers that were quoted verbatim from problem books without any hint of the source. Should we require proper citations in such cases - esp. when the poster is clearly copying verbatim from another source?
I really think the appropriate citations must be edited into the main body of the answers, or they need to be removed from the site entirely. The same thing goes for the questions. This is pure, cut-and-dry plagiarism and should not be tolerated. To put it as mildly as I can: It reflects poorly on all of us and it is unprofessional.
Absolutely. To me it seems incredibly rude to do otherwise. On MO this is less of an issue because grad students and professors in mathematics are already trained to cite sources constantly, but I think that habit is just as necessary here.
Apart from the social aspect, answers and questions alike are more useful when the relevant sources are cited.
Taking into consideration Quaochu's and Tom's answers, I explain my opinion and one example I would like advice.
Proper citations should always be done either in answers or in questions.
Plagiarism is intolerable.
I agree that in same cases (this is vage but I am not able to define them more precisely) there is a need to remove them from the site.
In my first question (the only one I've asked up to now) in the main site I quoted properly, I think, an exercise in a blog post, and indicated a proof of mine that was wrong to show that I had worked on it.
I asked the name of the theorem it referred to or a proof of it. I got a comment with the name of the theorem and a link to the site where several proofs are presented. Then one of the proofs was adapted (the notation was converted) and posted verbatim as an answer, citing the source.
In this meta-question I wrote: "Should my question on the main site be closed or deleted? I am not sure, but it may be
safer better to do so."
If anything has to be removed, please comment and/or do it and excuse this long explanation.