And even in specialist communities there is a certain degree of moderation needed in order to keep it in order.

In the offline worlds individuals for which (reasonable) moderation is needed are kept in check by society (either through social pressure or physical force).

Very seldom they are the beginning of societal changes but usually they are just unpleasant (e.g. "I hope you and your loved ones get murdered because...") people which most others avoid if they can.

I'm very sure I would leave any platform where their kind is allowed to run wild and so would many of my family and friends.

Facebook is a very good example: Most people are boring and nice enough. Those who are not (ranging from annoying to vile) spoil the fun for everybody else.

People leave (in part) because they don't want constant conflict and not every opinion is worth to be heard.