This is just incredibly wrong, though.
Music is full of people changing something, adding their own unique twist. (Example: https://ncjolt.org/blogs/olivia-rodrigos-music-copy. right-controversy/)
T.S. Eliot wrote an essay titled "Tradition and Individual Talent", where he succinctly addressed the problem of writing through inspiration. For him, Tradition was the collective installment of writing throughout both the historical past was a part of the contemporary future — a fusion between these tasks. The talent that held their own within this mix is a gesture toward the amalgamation of writing up to the point that the pen touches the page, to write. To even consider writing as a sense of ethical as a point to writing your own story is a load of bullshit, since there is nothing ethical about writing, it is either with ethics in mind or without it. Plagiarism relies on a body to sustain what is and what is not, and this might be a legal body or a public body.
Legal bodies pay attribute to the authors, vis-a-vis credits. This is easily done with, especially places like FanFiction or Ao3, to where credits are mentioned, but also have "Writer's Note" (or similar features included) to pay respects to the authors which they take from. This should be the only eligibility when considering ethics, the matter of respect that is paid. Credit where you get ideas from, if there is concern, but the dumb advice of "unique twist" is a load of hobwash than anything else, and that is more along the lines of "original idea". I don't want to write too much about this.
The matter of ethical is: Your ideas are always stolen, and they should be acknowledge that they are not original or unique. Pay respect to those where these ideas come from, include the idea if necessary. There is no ethical writing, nor will there ever be. Pay tribute, pay respects, pay homage, give credits. This is the one thing where "Footnotes" and "Citations" should come in hand; while it is not ethical, because writing itself is nothing ethical, it does enough to provide a point to know where things have come from. If your ideas are directly related to something else, put that information somewhere in your own story. If they are not taken from anything directly, they are "inspired by" or "adapted from", you can acknowledge this, but you don't need to do so. But your ideas are not original, nor will they ever be. This is Harold Bloom's idea of Influence of Anxiety, that to know our ideas are not original; we should be anxious in knowing that they are not, we should feel reprieve to doing so.
To write as yourself is to put this forward, the individual talent against tradition is simply writing. All of the tradition and influence from it come into part when the ink stains the page, when the letters hit the board.
This is the see for ChatGPT, except that there is no voice behind the mix; It cannot be held to the same standard as an individual. It is Tradition placed through a machine; there is nothing (read "agency") behind it. It mimics language and is programmed to do so, so that is a matter related to regulation instead of ethics.
Replying to some comments here, too.
Zama: "Plagiarism, on the other hand, is when you take someone else's work and pass it off as your own without proper attribution or permission".
You got there, halfway. If, in college or university, you submitted a piece that you originally wrote for another class for a different class, it would still be plagiarism. Plagiarism is doesn't need to have permission or attribution. If I take the phrase "Not all who wander are lost", it is probably not held to the same standards of plagiarism that an entire story is; there is clearly inspiration, but I also do not need to credit Tolkien for that line in an common story. I would get little flack for it, as well. It is still someone else's words.
Horu: "Technically, using something like ChatGPT isn't entirely unethical either is used properly."
Tell me exactly, in every instance, how to use ChatGPT properly. If you can, then I will take this as sage advice. However, because it is a tool, to use the tool is to use the tool correctly. Just by opening up ChatGPT is to use it properly. Now, if you want to have the thoughts are your own, then you fail in the attempt that you wrote what ChatGPT has displayed. If you take ideas from ChatGPT, the same this is mentioned before, and I will provide a sufficient example. Tell your audience you used ChatGPT, they might not like out, oh well, but ideas taken from this are ideas taken from a source and should hold proper respect to. The example here is from MLA citations.
The one thing that no one has ever said: If you think that your writing feels like a rip off, feels like you are stealing it and plagiarizing it, even you are not directly doing so, then mention that SOMEWHERE in your writing. Books often do this in the acknowledgements/copyright pages, songs will have this in the credits somewhere. Even Shakespeare left notes where to find where some of his inspiration came from. Include the information, the concerns, in your writing. If you have these concerns, and they are considerably warranted, and you do not include them, then your writing breaches on the unethical because you are are not writing.