And it's kinda funny how worked up we get over plagiarism in works of fic, which, uh, could count as such

See, I don't buy into that. Fanfiction writers make use of preexisting characters, but (a) we use disclaimers to credit the people who came up with those characters and settings and plots, etc., and (b) we are creating our own stories, not reprinting, say, a script from the show or a passage from the book and passing it off as our own. There's a key difference between copying and being inspired, you know? Even people who do borrow lines of dialogue from episodes or passages from books credit them in their author's notes.