No, people just like to share negative news. If there was a downvote button it would be closer to negative by design, but still not. Negative or positive could only be determined by content submitted.imho
There is a downvote button, it's just visible after a certain karma threshold, which moves up at the same rate as "karma inflation".
There's no downvote button on stories. That encourages people to leave negative comments, because they can't express their "negativity" by downvoting.