It's widely accepted that plagiarism is a bad thing. But why is this? What makes it wrong?

You might say that plagiarism is theft of intellectual property. To be sure, if I copy someone else's work and publish it myself, I'd be in breach of copyright; I'd be pirating their material. However, I think that the legal issue of copyright and the moral problem of plagiarism are quite distinct. I could pirate your work without plagiarizing it, if I made it freely available but attributed it to you. Conversely I could plagiarize without breach of copyright if the original work was in the public domain. Another view would be that plagiarism is wrong because it is stealing credit from the original creators. On this view the problem is that if you pass off my work as your own, then you're taking credit that's rightfully mine. You're making me a victim of your theft. This seems sensible. However, I don't think this is the only reason why plagiarism is wrong. I think that plagiarism's victims are not merely the original authors, but everyone else who is trying to produce original works in the same field. Plagiarism represents, so to speak, the counterfeiting of credit. It devalues the currency of creation. This is why "self-plagiarism" is wrong. On the "stealing credit" theory, there's no such thing as self-plagiarism: you can't steal from yourself, so you should be able to rehash your own work at will. However, surely if I copy my old work and pass it off as a new, original work, I'm getting credit twice when I only deserve it once. By self-plagiarizing, I didn't steal credit but I did counterfeit it (although other-plagiarism is even worse.) So plagiarism is not the theft of text, or ideas, or even of credit. However, I believe that plagiarists are stealing - at least, that is, whenever they find themselves in competition with honest people. Plagiarists steal opportunity from their honest peers. In science, for instance, jobs, promotions and funding are assigned largely on the basis of the publication records of the candidates. There are not enough of these things to go around. So whenever a plagiarist wins one of these prizes on the strength of their unfairly inflated record, someone else misses out. This is why I don'tlikeplagiarists. I don't take pleasure in anyone's 'downfall', but I look at it this way: for every disgraced plagiarist, an honest researcher gets a job, or gets funded, or gets promoted.