It works for the low effort, low interest stories. So the stuff that trolls might submit or stories that are otherwise uninteresting.
But what I'm referring to are the high interest, high flamebait stories. Which all of the stories I've linked are examples of where the discussion largely falls down along partisan lines and the end result is poor quality discussion. Then there are stories which fall somewhere in the middle such as this one, which are high interest but end up flagged over ideological reasons. One of the ways you can tell that is specifically the case for this story is because it's been submitted a number of times now [1] with a large amount of votes and a varying degree of flags.
[1] https://news.ycombinator.com/item?id=23870693
