I have seen good cops on TV and in movies. I have also seen aliens and dinosaurs on TV and in movies.﻿
It would be nice if the mythology about "the brave men and women of law enforcement," and the image of police seen on TV and in movies, in some way resembled reality. But it doesn't.
For example, when police show up en echelon with body armor, fully automatic firearms, armored vehicles and other riot equipment to a peaceful, non-violent demonstration comprised of unarmed citizen protesters who pose no physical threat, the police act like gang members because they are [effectively] gang members.
Cops join the police force/law enforcement for the same reason people join other gangs. Because they are cowards, who feel weak. Consequently they want to feel power over other citizens, so they join a gang which has guns (as well as myriad other armaments) to threaten, harass and otherwise 'gang up' on people.
Statistically, the occupational hazard of e.g. construction worker is more dangerous than being a cop.
Construction workers are also not generally know for for fatally shooting family dogs because they "feel threatened".