Downvote-type systems aren't that effective since they usually end up becoming a "I disagree" button and multiply the effect of whatever mob is most active at the moment. It's one of the reasons HN locks them behind a karma wall.
Even that is not an effective way to avoid the negative effects of the downvote button, especially not here on HN where it actually is meant to be used as a "disagree" button:
The "karma wall" only keeps the downvote option out of the hands of those who follow short-lived "mobs", it does nothing to stave off the balkanisation of the platform.
