I ran across an article that explains, rather well I think, the evils of plagiarism. According to Meghan O'Rourke, the problem with plagiarism is not that one writer is writing something unoriginal, but that he or she is piggy-backing someone else's hard work.
I agree completely with that analysis. The last thing I want is someone using what I have worked hard to write as their own personal shortcut to fortune and fame. Well, maybe that's exaggerating it a little, but regardless I don't much like the idea of someone else taking advantage of the hard work I put into my writing so that they can take it easy.