Have you ever spoke to a police officer? Outside of their job? They are the most terrified people I know. Jumpy jumpy. Constantly harping on how their job is the most dangerous in America (it is not). Carrying a gun around off duty, etc.
It is like a sickness. Something about the job takes people who are slightly inclined toward paranoia and drops them into a pool of it. They become scared of everything, suspicious of everything, and kind of lose connection with reality. It is not as bad as Q, but for a certain percentage of people who become police officers something about the training, the mentality, and the job simply messes with their mind.
People think they are getting off on some sort of power trip, but it is the exact opposite. They are terrified, and have been told if they are going to get shot as a police officer is most likely on an ordinary traffic stop. Every time they pull someone over it stresses them out, and sooner or later they just snap. A whole bunch of them are just terrified of everyone.