> But while downvotes seem useful for comments where there's a lot more scope for false information, trolling, etc., I'm not sure what the additional value woul

> But while downvotes seem useful for comments where there's a lot more scope for false information, trolling, etc., I'm not sure what the additional value would be for posts -- they're either popular or not, and you can still flag posts that are actively harmful. I think this ignores the concept of purpose. If you are optimizing for popularity, then this works. But a lot of forums (including Hacker News, theoretically) intend to optimize for relevance, which is contrary to popularity in many cases. For a really clear-cut example, Kim Kardashian's Instagram posts get far more likes than pretty much any post on Hacker News. Would Hacker News be better if it were replaced with a redirect to Kim Kardashian's Instagram feed? In terms of how popular the content is, this is an unambiguous yes. But that would not be a better Hacker News, it would just be more popular because you've replaced Hacker News with something completely different. That's an extreme example, but the same applies for content that's more relevant than Kim Kardashian's instagram feed. Popularity measures breadth of appeal more than anything else, so if you're trying to appeal to specific interests or cultivate some kind of niche content, popularity can be a negative. Downvotes can function as a way for a site's userbase to say, "Whoa, this is not what this place is supposed to be about, even if it is broadly appealing."