On HN, we have a small-ish community of people (who are often experts in a particular domain) and an expectation of on-topic, high-level discourse. Comment history is worth a lot here, as it's been vetted by an intelligent, serious community.
On reddit, you have a huge number of people and a very low expectation of what's acceptable to post (in general, of course--specific subreddits are often different). The relaxed atmosphere promotes users who tell jokes or pander to the large userbase, making it harder to identify users whose posts are worth actually reading through. Of course once you have identified a quality poster, it's nice to be able to go through their history. It's just that signals like karma score end up being meaningless at that scale.
Then there's 4chan, with opt-in identity. You can't inspect most users' histories, which means you have to take a submission at face value. And for serious, constructive submissions--admittedly hard to come by sometimes--this rivals the HN model for intellectually honest discussion. You're not just nodding along with well-known users, and you're also not ignoring submissions from people who may have simply slipped up in their past. But users can take a name if they choose, and there are 3rd-party archives which catalog their submissions.
I guess reddit just feels 'diluted' to me. It facilitates a broad range of discussion and does so fairly well, but I can't think of a subreddit that is actually the best place to discuss any particular topic. It's generally my second or third stop.
Well, it could be highly relevant, but the system isn't (yet?) designed to recognize when two sibling sites have significant overlap, which does occur.
Still true, but I think it is probably easier to allow controversial or less popular opinions in a ranked system than it is to deal with harassment in an unranked system, given the propensity of the voters towards "good." The harassment seen on reddit is very different from the harassment on Yik Yak, Juicy Campus, etc. That guy they thought was responsible for the Boston Marathon bombings, for example.
Of course, Yik Yak and Juicy Campus were designed for this LCD speech.
Persistent usernames on Reddit create a culture of identity on the site. Throwaways with no user history that post inflammatory comments frequently tend to get called out and downvoted. That's a very different setting from something like YikYak.
Are they not also more prone to being hell-banned?