One of my favorite subjects is woven through the highly entertaining This American Life segment about Emir Kamenica. I highly recommend listening. Unrelated to the main story, at the very beginning Michael Lewis details a very nice defense of plagiarism:
The concept was alien to me, I mean I just thought it was an odd concept because you repeat what other people say all the time, I was just repeating what someone else said, it was a very intelligent thing to repeat. And I thought I was saving us a lot of trouble… save him the trouble of having to read something really awful and I wouldn’t have to write a boring book report or even read the boring book and so I was doing both of us a favor. And it seemed sortof counterintuitive to have to generate a thing that had already been done.