J. Michael Straczynski (of _Babylon V_ fame, and many others) immediately blocks anyone who tries to ptch him ideas, and he's not the only one:
https://www.syfy.com/syfy-wire/j-michael-straczynski-would-l...
That's a problem with fanfic in general. People who would have written fanfic ten or fifteen years ago are writing stuff like litrpg's now; you can steal the general concept as long as you don't rip off the details. And it's a big enough world that you can practice your writing and actually become decent at it before you try to take on a big work. If you compare early drafts of, say, Dungeon Crawler Carl to the latest books in the series? You can see the skill improvement.
See for example the drama around Darkover fanfiction ([1], [2]):
Quote from [1]:
"For many years, Bradley actively encouraged Darkover fan fiction. She encouraged submissions from unpublished authors and reprinted some of it in commercial Darkover anthologies. This ended after a dispute with a fan over an unpublished Darkover novel of Bradley's that had similarities to one of the fan's stories. As a result, the novel remained unpublished and Bradley demanded the cessation of all Darkover fan fiction."
---
[1] https://en.wikipedia.org/w/index.php?title=Marion_Zimmer_Bra...
[2] https://journal.transformativeworks.org/index.php/twc/articl...
The alternatve is to do "cleanroom writing": you don't interact, therefore if you write something similar, you can argue you independently invented it.
I had the same problem in a scientific research lab where collaboration with another lab runs the risk of not being able to patent an idea, because if the other team had the same idea or anything close enough to it, we couldn't claim to be the inventors.
If I somehow recreated Lord of the Rings from scratch, without having known about Lord of the Rings, it wouldn't be copyright infringement because I never copied Lord of the Rings.
The issue is nobody would ever believe me when I said I coincidentally recreated Lord of the Rings from scratch. The court would conclude I copied Tolkien's books without permission.
If you admit to reading fanfiction, it reduces your credibility when you claim you independently came up with the same ideas as fanfiction authors.
This increases your litigation risk, but there's no black or white rule that you need to pay every fanfiction author or anything like that.
> The issue is nobody would ever believe me when I said I coincidentally recreated Lord of the Rings from scratch.
What do you mean? They believed Terry Goodkind; why not you?