I've been downvoted a few times and it was usually deserved. Also I had cases where initially it would go to -2 or -3 and then go up again to +2 or +3. Thus I can't confirm your observation of "blind down-voting". Sometimes a popular HN user will get a large amount of upvotes for comments that otherwise would probably attract less upvotes though.
Sometimes I really hesitate before commenting on a post,because I dont want to say something that might earn me a downvote, even when that comment might actually be right but might go against the trend of other comments on the post.