I understand that the best course of action is to add a source for a particular question. Is there a stronger way to encourage users to cite their sources in answers beyond down-voting factually correct but copied answers?
Simply copying information, word by word or big chunks of it, without citing the source is wrong.
I don't care how you see it or what license the information is shared from.
You should work the information that you obtain, adapt it and fit it to the needs of the site, after you did that you should add a link to the information you based your post on as the source.
Answers that are exact copies of information from other sites should not really exist in a good context, if you can edit them and make some use of that information great, else they should be flagged for moderation and possibly deleted.
Users that continuous paste information from other sources as their own answers will be warned and possibly have their accounts suspended.
I do that sometime. Reason, I don't know much about Ubuntu, and Linux fro that matter, and I know that is not an excuse.
The first rule of copying information from a location to another is to identify the owner. By doing so it is not considered plagiarism. Now copying and changing few word, is still called plagiarism if you don't cite your source.
I try to be Conscientious about what to copy and include the site that it was copied from, just to avoid such a dilemma. I sometimes go back to plagiarism.org in case I get worried about something, and I try to research it. Sometimes I even ask the professors at the university that I work at on how to copy information, and use it without committing plagiarism.
Bruno Pereira said in his answer "Plagiarism without citing the source is wrong" well if you cite the source is not plagiarism, you are merely copying the words verbatim.
Don't miss understand me I agree with Bruno Pereira, you should try to put thing in your own words, but that doesn't relieve you from citing. You still have to cite the source (website) and sometimes that author or creator of the information that you are trying to use.
I hope that all of us here would work in harmony, and help each other in any way we can if possible. I remember asking a question about down-voting earlier, and it was closed as being a duplicate, I looked at that question, and one of the answers said " votes are anonymous, so you should not have to reveal your identity when you down-vote" Gilles.
I agree with that, but there should be an option of multiple reasons that you can choose from, and I think that may help that person to improve his question/answer. I don't know maybe I went off on a tangent here, but lets all work together as one.
Perhaps adding a script to the site that detects pasting of blocks of text over 150 (tweet-length) characters, and prompts an in-site pop-up with "Is this copied from an article?", reminding you to cite your source. For many people it may sadly just slip their mind, and this plagiarism may turn out to be negated by such a reminder.