I would vastly prefer private security forces to provide defense for me than the police. History is full of examples of neighborhoods and ethnic groups organizing their own defenses to manage misbehavior from within and without those groups.
The existence of police dramatically harms the possibility of an ideal society, because they do so much violence with such immunity.
You seem to think that I believe that the status quo is somehow acceptable or tolerable.
This is like saying 'if the US military didn't initiate war against another country, how would it ensure compliance of that population with the wishes of the United States?'
Obviously the answer is to not go to war, and not concern oneself with whether or not another population is sufficiently compliant.
The full and detailed answer to your question is outlined in a book titled 'The problem of political authority: and examination on the right to coerce and the duty to obey'