My idea is that if the user karma was removed, and upvotes on links were used to merely weigh and sort links, and downvotes on comments were removed, Reddit, and also HN, would improve. Many attention seekers spam many subreddits, and also HN, merely for the karma. Instead, give users some lives, as in games, and each time the user is seen spamming/harassing, take away a life, and when he runs out of lives, ban him. Though I have no factual experience to back my thoughts, but mailing lists and bulletin boards are mostly run similarly to what I describe.