> In the fact that you didn't write it.

This is a fact and this is generally not a problem. Customer support guy Joe did not write that email to you with a refund: someone else did it and Joe did pick the template. Alice did not write that post card to Bob, someone else did and she just googled some nice text. We deal with a lot of content that wasn’t written by the person who signed it. That content, when written by LLM, may indeed contain watermarks and nobody will care about the choice of words, because only the meaning matters in such communications.

People pay too much attention to authenticity here, which is no more than a demonstration of an effort. LLM can and should write scientific articles because the real effort is in directing research, not summarizing it. LLMs can and should write news, because it is cheap and efficient, and real reporting is in discovery. LLM can and should write fiction and make movies, because there is no reason why creators of various junk should earn their money easily. LLMs do not replace real talent. They just emphasize for an average person how easily replaceable they are. And that‘s ok. Creative industry is a blue collar job now.