If you've ever worked closely with someone else in a work environment (so pretty much everyone), you've had a disagreement. Maybe you didn't agree with the current approach for tackling a project, or you weren't quite sold on the marketing of a new product.
Many find themselves arguing with someone on the Internet, especially in these days fraught with political tensions. A great tool, the web also seems to drive dispute. It is also a reflection of the larger reality, where divisiveness has spread throughout our society.