When most people skip the meeting, those who are left tend to be more extreme, because they care more about the outcome

If participation in political debate declines - if fewer and fewer voices engage in democratic debate - our politics will become more shrill and less balanced. When most people skip the meeting, those who are left tend to be more extreme, because they care more about the outcome... The correlation between ideological "extremism" and participation strengthened over the last quarter of the twentieth century, as people who characterize themselves as being "middle of the road" ideologically have disproportionately disappeared from public meetings, local organizations, political parties, rallies and the like. In the 1990s, self described political middle-of-the-roaders were about one-half as likely to participate in public meetings, local civic organizations, and political parties as the mid-1970s... The declines were smallest - averaging less than one-fifth - among people who described themselves as "very" liberal or "very" conservative.

D. Putnam, Bowling Alone (2000), 342

Prescient.