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Pluralistic: "If buying isn't owning, piracy isn't stealing"
(pluralistic.net)
This is a most excellent place for technology news and articles.
Plagiarism involves an extra act of deceit. You're passing off someone else's work as your own. It appears most people find this immoral.
Also, copyright is a monopoly on the publication of the work - piracy as it's commonly used wouldn't even be considered infringement.