Plato is of the opinion in his Republic Book X that all writing is copying. And not mere copying but one that's thrice far from the truth (which exists in the world of forms)...remember his Allegory of Caves? Aristotle on the other hand in his Poetics does not see anything wrong in writing representing what exists in reality. He even says that creativity lies in that act of re-presenting.
In our world, copying takes several forms--from the echoes of writers read in the past to literally going on Google to yank off articles (what we call cut and paste!). Some also echo various thoughts and ideas from previous writers while some just go onto other people's blogs, website or into their books to yank off their works...mark it without permission. This reminds me of the battle between Molara Wood and Africa's Best Stories Supporters. When and where in the world do people have the right to add your story to a collection without your permission till after the book has gone to press?
I also remember reading a quotation sometime ago by Wilson Mizner:
“When you take stuff from one writer it's plagiarism; but when you take it from many writers, it's research.”
Where does copying end and plagiarism begins? Where is copyright infringed? And maybe it would be good if you share your thoughts on how writers can protect their work online....