I think all students at police academies need to be informed that they don't automatically merit respect because they wear a badge. They EARN respect by their behavior when dealing with the public. That isn't to say they can't be firm; I understand that a firm and direct tone helps to deflate dangerous situations. But there's a difference between speaking firmly and being randomly abusive.
And, no, I have never had a bad experience with a police officer, not even in the deep South. I have always been approached respectfully and have responded in kind. But then I'm a white male.