It's not unique to reddit but it is definitely exacerbated by the upvote/downvote system. If one side of a discussion becomes even just a slight majority that side can essentially silence their opposition, once one side starts to get traction it gains exponentially more because their slightly favored posts go to the top and get even more views/votes while the slightly less favored posts go to the bottom or get completely hidden. As soon as a narrative starts to form everything else is obscured. IDDQD, TwoEasy and Talespin have all fallen victim to this.