Comment by staticman2

It's not that you have to pay everyone with the same idea, it's that it opens you up to claims you copied fanfiction writers you never copied.

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.