I have never thought that vigilante groups are a good idea.
What seems to be a valid course of action by concerned members of society can all too often by hi-jacked by the unhinged who enjoy the 'gang' mentality, are so self-righteous it's almost painful, and quite enjoy venting their repressed anger in systematic violence against people who have not been proven to have committed a crime.
I always think of the plot of Clint Eastwood's Magnum Force, released way back in 1973, where vigilante cops were 'cleaning up the city' - as Clint's Dirty Harry character wondered, where does it stop? 'Before long you execute your neighbour because his dog wees on your lawn (not the term he used!) and that is exactly what we have to be aware of.
Society is full of people looking to 'belong' to something because it addresses their feelings of inadequacy and isolation. That may be something as harmless as the local golf club committee, or as scary as the local paedophile-bashers collective, but the thread that runs through all these voluntary organisations is the often-encountered factionalism, back-biting, vendettas, power struggles, and so on. If you add that scenario into a group who are wandering the streets with pick-axe handles, you have something really serious to deal with.