Isn't the point of the police to have a monopoly on violence?! I mean, I'm sure Walmart could create its own army if they had to, but ... do we, as a society, really want that?
Not sure about an army, but I think the point is that they are actively consuming a public service more often because they have cut their own costs, instead of paying for a deterrent themselves.
I don't believe that anybody has suggested that. What people have suggested is having more staff present, like Walmart used to have. Police aren't the only way to stop crime. They aren't even the best way.