When I was a teenager (early '70s), my older Bro-in-law was a Sergeant on the Denison (TX) police force, and "Cop" was considered very disrespectful then.
Times change, and so does the language.
At one time, cops were peace officers. In most small towns that was the case until recently. Big cities have historically been occupied by a more militant, adversarial force. (often rife with corruption)
Today LEOs seem to have that us-vs- them mentality more often than not. It's a shame really. Cops are a necessary evil, since people are imperfect and prey on each other. Maybe someday we can eliminate the victimless crimes and the enforces of such can go away too. Maybe respect for actual peace officers could be restored.