Police are supposed to behave in a certain way, and so are citizens. When one or both misbehaves we have chaos in varying degrees.
Ferguson -- young men when asked to walk on the sidewalk instead of the street should comply. Police officers should never let situations escalate. Officer f-ed up. Communities shouldn't tear themselves apart or allow others to.
Reporters in hot zones should have more street smarts. And making the story about the reporter instead of that which is being reported upon is not the best example of quality journalism.
Have I ever had a "negative" experience with a police officer while taking street photos? Yes. I was photographing some FDNY paramedics assisting a homeless man. There were several police officers present, and one had a bug up his butt, and told me not to take photos. I knew my behavior was legal and took a few more shots. He gave me a dirty look. If I were in an isolated area I wouldn't have taken more photos -- because being legal wouldn't have helped me -- the reason being this particular officer was in a bad mood.
I've photographed police officers in NYC without problems. I will often ask if they mind -- because they might work undercover and not want photos of themselves in uniform lest their cover be compromised. Trying not to be an a-hole is a good policy -- but if the photo is good -- I mean too good not to shoot, then as a photographer, that's that for me. We do our best to read the situation. Being right isn't always worth the effort.
The worst people regarding threatening or "hating on" photographers I've found to be other photographers.
Bottom line: Whatever, that's life!
The public -- yeah, a great many are ignorant of the laws regarding street photography. I won't be surprised if sometime in the not to distant future, the laws are changed making street photography illegal, or severely compromising same.