Once in a while I see the Worldbuilding site.
But if answers from this site literally become integrated into books, games, movies, apps and so on, how does the user of the answer avoid any claim to copyright infringement?
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Worldbuilding offers ideas and "[c]opyright does not protect ideas". Even with the best of legal teams, in most cases I doubt that there would be anything to go after, legally.
A user would have a valid complaint if the license is not being followed, such as if their exact words were used without crediting them.
However, most users are unlikely to have even thought about this. How would you know someone was copying you in the first place? What do you expect to get for your work that you essentially donated to the internet for a chance at internet points?
A lot of copyrighted content lives on in posts either because of fair use or that the copyright holder just doesn't know or care that their content is being used.
But sometimes they do care. The copyright holder can submit a DMCA takedown and their content will be deleted from the site if it's deemed a valid claim by Stack Exchange employees. This is rare but it does happen. For example, Post deleted due to DMCA notice on Stack Overflow. However, because it's done through deleting or redacting posts, it's unlikely that a regular user would notice a takedown. Even moderators wouldn't be involved with this process (except maybe to help users find the right way to submit a claim), though they would be able to see the takedown happening if they were looking in the right place.