That's not true of every country though, it's certainly not the case in the UK. Here the police do act as your friends, they make a lot of effort to talk to the general public, both on the beat and at events. Certainly every encounter I've had with the police has been positive, even when I've been in the wrong (speeding or whatever). Police can be your friend, they can be accountable and they certainly don't need to be prone to violent outbursts.
The basic upshot of this story is to keep your contact with the Police brief, friendly and say no more than you need to.
The Police have been doing this to black people, gay people and other minorities for years, it's actually quite ironic that the Stonewall riots happened in San Fran too.
All that's happened this time is a well off, straight, white chap has realised just how hard life gets when you're treated as a minority.
I hope he gets his day in court and if the story is true they will sort the copper out and pay some compensation to him.