The groups need an established core of well informed and experienced people to work together and shape the culture of the community. The moderation team also needs to be responsive and consistent.
I got pulled into being part of one of those teams years ago. It was a pretty simple formula to make the community healthy: The creeps/spammers got banned and reported. The ignorant got educated in a logical and coherent manner by a team approach. The trolls were played with for a while then banned when they eventually violated a rule.
A good group can save lives and help a lot of people. A bad one can further harm the already damaged and vulnerable. There are many of both groups out there.