[paganel]

It's mostly because on the Internet you can self-select (sort of) your topic of discussion and your "social" circles.

In real life it would be difficult to have a "fight" and a discussion over public transportation or some random history subject, because, presumably, your friends from real life are not that interested in those subjects. But if you are interested in those subjects you most probably frequent places on the internet that discuss them, hence the fights and the discussions.