Facebook has said that they don't want to put in features that would discourage participation. If someone updates their status and lots of people "dislike" it, they might not want to update their status next time.

For HN, I'd like to see a "track it" button - I don't want to upvote a lame article but often the HN community has a lot of interesting things to say so I'd like to keep track of those article's conversations.