I suspect a big part of it is being in an echo-chamber of people who have almost the exact same set of beliefs, which are then contrasted with the more extreme opposite beliefs. This creates a rather simplistic (and therefore desirable) us vs. them dynamic.

I've experienced this as conservative christian, and I only realized how black and white my world-view had become once I 'got out'.

I could be wrong though. I generally avoid these 'communities' for the reason the author describes.