The problem with a full range rating (positive and negative) is that over time people will abuse it. We've seen this on an older web project (http://www.trendbuero.de/dk/). If you have a negative rating sooner or later little groups in your community will emerge and they will try to dominate everyone with their taste. They will call their peers and ask for downvotes. And when someone get's a lot of downvotes for a post it's unlikely that he will ever post again - he's scared away - forever. In a just positive rating system: If someone does not get any likes, he'll try again - maybe with different content. So traffic wise it's besser to just allow positive ratings.
Comments
The problem with a full range rating (positive and negative) is that over time people will abuse it. We've seen this on an older web project (http://www.trendbuero.de/dk/). If you have a negative rating sooner or later little groups in your community will emerge and they will try to dominate everyone with their taste. They will call their peers and ask for downvotes. And when someone get's a lot of downvotes for a post it's unlikely that he will ever post again - he's scared away - forever. In a just positive rating system: If someone does not get any likes, he'll try again - maybe with different content. So traffic wise it's besser to just allow positive ratings.