It's called citing your sources so that the site doesn't get into legal trouble for plagarism. If you guys cannot respect the standards for the site that have been established for years, then please find another site to contribute to. I'd rather everyone stay and have fun, healthy dialog about our favorite team and players, but the continual ignorance of standards and the counter attack against those that ask you to respect those standards is not congruent with the goals of this forum. Please cite sources with a link, provide a short clipping (for context) from the source and then start your discussion topic.
Most sites have that in the TOS, although I doubt a non-profit fan forum would get sued for plagiarism for not having a link. My own opinion is that I appreciate people putting them in for for the reasons you stated. I have never seen it become an issue anywhere else.
The problem with believing that it is unlikely a non-profit fan forum will be sued is that it relies on assuming rational behaviour on the part of the person who was plagiarized (or otherwise offended). When people get offended they get angry. Angry people do irrational things, especially if their pride has been hurt. Its just safer to not poke the bear.