So my problem with this example is that Detroit isn't safe, if you step out of a protected neighbourhood.
I think the point here is: The protected neighborhood is, well...protected. And it's protected by private security.
That's a positive sign that private security is not only possible, but that it can be successful/profitable without any need for coercion. And the private security companies are actually accountable to their customers. If they went around harassing, robbing, beating, and/or killing their customers, they'd probably be out of business in a hurry.
I dunno about you, but I heard that beating and killing your customers is the best way to get repeat business.