What you're saying about the pressures on police officers is true, but the conclusion you draw from it is not. It is not actually the case that police officers must be managed in such a way that their professionalism is degraded by contact with the worst parts of society. One can think of many kinds of management interventions that could mitigate this problem --- or, for that matter, read books about modern police patrolling and the day-to-day work life of police officers to see good ones already written down.
I liked Moskos "Cop In The Hood", as a quick easy read; a lot of the rest of what I've read are cop blog posts or policy papers.
Two good example of problematic management techniques:
* All-car patrols, where police officers are either locked into their squad cars or, if out of the car and not eating lunch, in some kind of scuffle, so that their only contact with the locals is bad.
* Triage coverage, where units from all around the city are swung to hotspot areas in the city (in Chicago, for instance, alternately the west side or the south side), so nobody puts down roots with the community.
There are others.
A theme to all the recommendations I've heard is that they cost money. It costs money to allocate patrols so that officers can take the time to be on foot and retain the same neighborhood coverage they had before. It costs a lot of money to allocate enough officers to simultaneously and permanently cover the hotspot neighborhoods.
