Depending on who you ask around in SHTF & Hurricane Katrina… law enforcement were helpful… a threat…or a bit of both. In SHTF scenario law enforcement conduct will probably be all over the map particularly in urban settings that are a powder keg already (e.g. gangs). Many municipalities struggle to fund police departments which often impact morale among their officers. A family friend was (now retired) a high ranking police officer in Dallas PD and I heard an earful from time to time. It’s like any profession good apples and bad apples.

Dallas PD survey:
“They commented after 80 percent of the 1,279 officers who took the survey rated their own morale “low” or “the lowest it’s ever been.” The respondents account for roughly a third of the department’s 3,500 sworn officers.”
http://www.dallasnews.com/news/metro/20140731-dallas-police-association-survey-finds-morale-is-low-among-officers.ece — Whatever their reasoning for low morale…it will play out in various ways in SHTF.