some people (1) have a compulsion to speak, (2) don't feel as much cost from (online) admonishment, and (3) have enough wherewithal to experiment with ideas and presentational approaches. (i'm sure there are other qualities, but these are some).
on another tangent, social cohesion requires that a certain number of people incur the social costs of calling out bad behavior. that seemingly tends to be power law too, since the number of people who don't mind the social costs are quite low. even many law enforcement officers (whose very job it is) care a lot about what other people think and won't always act against self interests when necessary.