Private security has been demonstrated to be more effective at preventing injury and damage, and less damaging to communities than traditional government funded and controlled 'law enforcement'.  For instance,  Threat Management Center in Detroit did a marvelous job of actually protecting people and their property after the government basically shut down in the city after the 2008 crash, and they managed to do it without accosting people who hadn't hurt anyone else.

The government militaries waste incredible amounts of resources and accept people to work for them who would never get a job in a good private security company. While there is plenty of nasty merc companies they call PMC's there is no reason why they have to be like this, it is just what the government wants, since the cost is much lower to deploy them.

I live in Bulgaria and private security companies have a very big and visible presence. The state police forces are absolute rubbish. There is a big problem in this country as is common in all of eastern europe, of Gypsy thieves stripping buildings and building sites of resellable materials, and the private security do a very good job of keeping them at bay.