In my opinion the issue is that there's a conflux of things, some of which are based on morality and some aren't. Morally, everyone has some sense of what they think is right and wrong, and some sense of when they should stop someone else from doing something they think is wrong (in some way, not necessarily physically preventing them but taking action against them). However, there is a third part of this which isn't really about morality but about personal satisfaction, effectively some people really get off on imposing some amount of power over other people. To the people who go out of their way to report the site, they are getting satisfaction out of preventing someone else from doing something they think is immoral. There's obviously degrees of all of this, you'd probably get some satisfaction if a robber you reported to the police was caught too, but the kinds of people the Internet now calls Karens get a lot of satisfaction just by imposing power on other people, even if there's no real gain to them.