Nick Rekieta talked about this recently. The power to police comes from the people, as all government power does. When the government fails to exercise that power properly, vigilantes are inevitable as people will not stand for justice not being carried out. Per Rekieta, it's exemplified by the Punisher, who represents the spirit of seeking justice in an absolute way, rather than the process that the State is forced to follow in order to ensure the State doesn’t go overboard with excessive power.