The State of Play, page-2

Forums usually require that you register or take the time to type out your thoughts. As a result, the only people who tend to bother doing such a thing are people who feel particularly positive or negative about something. All of the people who feel neutral or only slightly lean one way or another, get lost because sharing their opinion is not worth the investment of time and effort for them.

In this way, forum discourse self-selects for the most extreme viewpoints. And unfortunately, only being presented with the extreme viewpoints in any situation, causes our views to diverge even further.

The debate becomes defined by the extreme minorities, while the silent majority in the middle either checks out entirely or gets sucked into one extreme viewpoint or the other.