No one is denying that good cops do exist.
The problem is that (especially for minorities in large cities) calling for the police is a gamble.
That many white, suburban kids are taught from a young age that "all police are your friends, you can always go to them if you need help" and that many minorities in cities are taught from a young age "cops are people near complete immunity, great authority and guns; they are to be feared; you would do best to avoid them at all costs and if you must interact with them, be as non-confrontational as possible and if you are arrested say nothing until you have a lawyer".
From the article ...
> I was standing 15 feet from the scene beside Officer Kaur, a stocky female of South Asian complexion. She turned to me and abruptly said that I was not needed as a witness and should leave immediately. I told her we were headed home, just across the way, when my friend and I encountered the accident; and that I’d recently broken my elbow in a similar bike accident here and deeply cared about the outcome.
The cop told the author to leave, the author indicated otherwise.
I guess the author got the "police are your friends" story growing up, not the "avoid at all costs and be non-confrontational if you cannot" story.
Every time the author got confrontational, the situation worsened. Want a doctor? Solitary.
From here, the next thing is "but what about the author's rights? even if the cops don't like you, you still have rights!". Sure, and exercising your rights is inconvenient, at times requiring things like going to jail until things are sorted out.
For a cop arresting you, it's just another day at work. For you, it's missing work unexpectedly, maybe some legal bills, worrying who is watching your kid in a few hours, etc. Your life goes upside for a bit even if charges are ultimately dropped or if the first time in front of a judge your lawyer convinces the judge to throw out the case. You have everything to lose and they/the system/etc. have nothing to lose (except for once in a while when it gets really bad and there's a huge lawsuit, like this recent local story[0], unless you've got some clout, in which case the mayor will call to see how you're doing[1]).
[0] http://www.nytimes.com/2014/01/27/nyregion/man-51-dies-in-th...
[1] http://www.nytimes.com/2014/02/14/nyregion/de-blasio-defends...