Because an armed civilian who takes care of a criminal by shooting him, makes the police look incompetent by comparison. For example, if we are armed and walk down the street and witness a robbery - we can fire on the robbers if they begin to point their pistols in our direction. We don’t have to yell “Police, STOP!” before we fire. We don’t have to negotiate, we can simply ‘defend ourselves’ and blow the bad guys away.
We can unload on them before they hit the ground. We do not get a ‘review board’, we do not get ‘police brutality articles’, we do not get the felon’s parents telling the community how their boy was really just ‘misunderstood’. We get a parade, handshakes and pats on the back.
We go to work with people calling us heroes behind our backs. We get respect, and honor.
A policeman is called a murderer, a sadist and a bully. He gets a review board (who may never have been shot at, or walked a dangerous beat) to question every witness, and then if they have been proven innocent - the police have the distinction of being allowed to continue their employment.
So, I can see why they may not like the competition.
Well, chiefs tend to percolate upwards toward larger cities, so an anti-rights attitude must be attractive to those who hire chiefs in large cities. Being against the citizens is good for your career if you’re a police chief. How’s that for irony?