As a general rule, cops can’t act. they can only react.
They can not for example cordon off several blocks odf Chicago and gather up all the Trayvons and take their guns. That would be illegal search and seizure. They can only act by investigating the shooting. murders.
To beg for action is to beg for loss of freedom
I'm much more comfortable with people walking around with guns -- strangers will tend to be polite. We just need a broad understanding of such things as Castle Doctrine and Stand Your Ground. Initiation of Force is a bad thing, once someone initiates, then they should become fair game for any citizen.
Back in the day of the beat cop, when the officer walked the streets, talked to merchants, and knew when there was something out of place, that was positive, proactive law enforcement.
Now they huddle in their Bearcats until 3:00 a.m. when they conduct no knock raids on people who bought one too many sunlamps :/