AFAIK, Copy-pasting the whole Article is not fair under 'Fair use'
http://www.copyright.gov/fls/fl102.html
How much of someone else's work can I use without getting permission?
Under the fair use doctrine of the U.S. copyright statute, it is permissible to use limited portions of a work including quotes, for purposes such as commentary, criticism, news reporting, and scholarly reports. There are no legal rules permitting the use of a specific number of words, a certain number of musical notes, or percentage of a work. Whether a particular use qualifies as fair use depends on all the circumstances. See FL 102, Fair Use, and Circular 21, Reproductions of Copyrighted Works by Educators and Librarians.
And leaving aside legal aspect, its also not fair from moral point of view. Its a subject of debate though.
Why people do not like their Full article to be copy-pasted ? They want people to visit their blog/site. So its best to provide a portion of article and provide link to the main article saying "........Continue at Source" OR ' ..........Full Story at source"
Many of us do not know and so they must have done that. As people will learn about it and thus they will follow that Courtesy rule, that's what I think.
Also I will request members not only to provide copy paste part of articles but also read other article links provided by other members on the MW forum thus eliminating duplicates. So provide your articles and also read other articles thread put by other active members.