It's worth noting that reddit is a big place. The majority of subs are largely free of this nonsense - it's the accumulation of it all that makes it look so prevalent.
I only noticed what was up when The Verge wrote an article on it, for example, since I tend to browse subreddits directly.
It would be more accurate to compare Hacker News to a single subreddit than it would to compare it to reddit as a whole. Like reddit, hacker news has it's own rules and tolerances in place, but reddit as a whole attempts to leave censorship up to the subreddit moderators.