I think we may be arguing over semantics.
Let's say you decide to write a story about a boy wizard who battles dinosaur ninjas trying to take over the world.
That's the idea. It doesn't matter whether you came up with that idea on your own, got the idea from an old B-movie, read it in an AI-generated story or saw it in a forum post.
Now, if you go and write such a story, I can say, "You stole my idea!" And, yeah, maybe it doesn't look good, but ideas aren't protected. Once you put it out there, anyone can run with it. That's why a lot of us keep our stories secretive until they're finished and published. We don't want people "stealing" our ideas but we also know there's no way to protect those ideas.
And, the truth is that if you and I were to both write a story about a boy wizard battling dinosaur ninjas, those stories are going to be wildly different. Still, even recognizing that, you want to be the first to release such a story.
Of course, inevitably, you'll probably find that someone else had a similar idea years ago that you didn't even know about, so sometimes it just comes down to timing. That is, getting a story out after any similar story is long forgotten but before anyone else releases something similar.
Because there's also the possibility that two people can come up with a similar idea at the same time. I know that's happened to me and, because I'm a slow writer, the other person finishes first and then I put my story on the backburner so I don't look like a copycat.
So I don't have an issue with the source of the ideas.
The issue, I think, is who is actually doing the writing. I don't think we need to rehash the issues with AI-generated writing (plagiarism, copyright infringement, etc.). If a person does the writing, I don't think it matters whether a particular idea came from that person or was part of something AI-generated or whatever. If the writing is the expression of a human writer, then there is no problem, even if an idea came from AI.
But, if the AI is doing the writing, then there's the issue. I mean, you could feed your ideas into AI and end up with something that infringes on someone else's copyright if the AI spits out verbatim something someone else wrote. So, I don't think the source of the ideas matters. It's the expression. And if that expression comes mainly from AI and not a human, then there is an issue.