Cops provide plenty of red meat for the cop-haters, and there is a wealth of stuff filmed and put on the internet every day that is totally inexcusable and rarely met with any judicial reckoning. Prosecutors are understandably reluctant to destroy the credibility of an entire force over a bad actor and cops have a very strong professional ethic about closing ranks to protect even their own worst by silence or denial if not outright falsehood, so indictments are rare even in extreme cases, let alone convictions.
Unfortunately, all this has the effect of enraging the populace against all of them when the story of the abuses gets out anyway, and the good cops that closed ranks to protect the stinkers end up paying the price when the whole thing reaches critical mass.
And yes, sadly, cops aren't any more honest than anyone else on the stand, as a prosecutor I've had cops whose cases I wouldn't take to court because I knew they'd testified falsely in the past and I wanted no part in putting perjured testimony forward.
