Which, if ChatGPT has or is getting parity with human writers then, by definition, it’s going to be impossible to tell the difference.
And if it can tell the difference it’s either going to prove their product is substandard, they can identify snippets of copyrighted material they have in their training set, or falsely identify people whose content and styles their training on.
I’m not sure what the angel here is for OpenAI but it’s problematic to their brand and, potentially, legally no matter how they go about it.