I am not very versed in those legal matters but I imagine there is a whole spectrum between Facebook (where all your content is personal and you should be able to take it out as needed) and Stack Overflow or Wikipedia (where taking out answered questions or articles when an author wants it doesn't make sense). I wonder how this is regulated, especially in regions with "strong" right to be forgotten e.g. Europe.

More than once I have stumbled on deleted Reddit comments that looked to have something I was looking for. Maybe it's good that the right type of content is posted in places with the right kind of deletion rules, but this should definitely be advertised clearly (so people don't start Q/A type subreddits, and conversely don't post personal info on HN).