Mistake theory on plagiarism:
How is it that capable thinkers and writers destroy their careers by publishing plagiarized paragraphs, sometimes with telling edits that show they didn't just "forget to put quotes around it?"
Here is my mistake-theory hypothesis:
True - "harm reduction" is a tactic that helps with negligence or mistake, and less so with true adversarial situations. It's worth remembering that improvements are improvements, even if only for some subset of infractions.
I don't particularly worry about plagiarism very often - I'm not writing formal papers, but most of my internal documents benefit from a references appendix (or inline) for where data came from. I'd enjoy a plugin that does "referenceable copy/paste", which includes the URL (or document title, or, for some things, a biblio-formatted source).