Precisely. There's intervening because you are at the right place at the right time. There's coordinated efforts like citizen patrols and neighborhood watches. In those instances, people are acting as fellow citizens for fellow citizens. They can be called as witnesses if needed. The moment someone puts on a mask or actively goes looking for trouble, then things can start getting dodgy.

I'm not saying vigilantes can't do good. A friend of mine was saved from a very dangerous situation by one, and I'm extremely relieved he was. I can't help but be concerned about what could happen if that vigilante were to get out of hand.