The problem with group moderation is that it will form disparate, isolated groups that get larger over time. This gradually reduces the effectiveness of democracy and destroys social cohesion. The people in the same group see other groups as more and more evil as the groups get larger, so they don't talk to eachother as much. The effort required to talk to people in a different group becomes larger as the groups get larger, so fewer and fewer individuals are capable of dialogue, until eventually, there are just two echo chambers that absolutely hate eachother. And what follows is either violence or oppression, or both, because the conflict has reached the government level.
There used to be a cap on practical group size before the Internet (except in rare cases, those become authoritarian states), so this went unnoticed in democratic societies. But now there isn't. We ought to consciously realize that the base unit of a democratic society is an individual, and create policies that enable decisions at the individual level.
We ought to talk to people that we think are evil. And let them talk, too.