I think the problem with 'modern' policing, at least over here anyway, is that it's focused around going through the motions of investigating crimes (after they happen) for the purposes of meeting targets, rather than providing a real visual deterrent. Which is why the poorer areas have now become run down and crime infested. Near to where I live, gangs of thugs now control the streets at night. People are afraid to go out late, public transport is also dangerous at night - welcome to 21st century urban Britain.

For the purposes of this visual deterrent, private security could fill the same role and at a far lower cost. The problem is that private security will only be there for those that can afford it. In a nutshell, those poor areas will still as dangerous as ever, while the well to do will have gated communities and private security guards.