When the authorities do not protect the citizenry from criminals, or worse, take the side of the criminals against the citizenry; and the citizenry cannot replace the authorities through elective means; vigilantism may appropriately result.
Vigilantism rarely begins with violence, except to stop a violent crime in progress. It typically begins with a petition for redress to the authorities, which is ignored.
Then there are individual and group efforts to protect themselves from the criminals, which either the criminals overcome on their own, or with the help of the authorities are discouraged, such as with legal gun control efforts, so that only the criminals and the authorities have guns.
Only at this point does a vigilance committee form, but it is still nonviolent, creating block watches, which are opposed or attacked by the criminals and authorities. At about this point, the authorities determine that the vigilance committee is a real threat to them and their criminal allies, so they seek to outlaw it, and arrest, beat or even kill its leaders.
Only at this point is the vigilance committee driven to violence, but even then, only to drive the criminals out. But if the criminals and authorities resist, the vigilantes become a violent mob, hanging those of both groups with a lynch mob.
Typically the event is over before superior authorities arrive, having determined that a problem exists. At first they want to arrest the responsible vigilantes and restore the existing authorities, but by now neither thing is possible.
Order has already been restored with the criminals gone and new authorities soon take the place of the old, corrupt ones. The vigilance committee becomes invisible and inactive.
Well one thing for sure — parents need tosend their kids to school armed with poptarts and the knowledge of how to turn them into popguns.