If we're all bunched into small communities, there is no 'at scale'.

I regularly hang out in several different communities of thousands of people, including this one. All of them, except the really small ones, have one or a few people who moderate the forums, and ways to report things that are posted. If someone posts a link to disturbing video to HN, it's going to disappear right quick; even if the source lives on. If I try out a community where there's a lot of disturbing videos posted, I'm going to stop going there; but other people might go there specifically because of those video links. If the videos are legal, that's their business and none of mine; I don't want to see it, and by avoiding their community, I won't.