

Does it count as vigilantism? That’s subjective, dependent on the definition of vigilantism.
Is vigilantism generally a good or a bad thing? It’s bad. A justice system needs to be designed to be just, which is why we separate the roles of police, jury, and judiciary. The intention being to develop fair and just outcomes. Vigilantism has no process.
Someone just arbitrarily determines someone’s guilt and punishment.
There’s a variety of reasons.