Well, most vigilantes are treated as criminals, or rather- vigilantism is usually treated as a criminal act, so they would have all reason to shoot us on sight.
The actual question here is how do we respond to that assault. Can we run away or do we have to fend off the attack or reason with them. It will depend.
EDIT: I mean, that is sort of the idea here. Do lawful acts outside the boundaries of the law. Be bad for doing good. Or rather, what the characters think is good.