It’s just the default stance. Kind of like assuming everyone on the road is a bad driver and driving defensively as a result. It’s safer to assume every cop you interact with is actively looking for a way to screw you over, will lie to you and will violate your rights given the opportunity. Even if it’s just most, or hell even rare that cops are bastards it only takes one interaction with one to have life altering consequences.
That way you can defend your rights and be pleasantly surprised on the rare opportunity you encounter one who isn’t a bastard, rather than be constantly disappointed (and possibly in jail or dead).
It gets better. The cops didn’t receive any punishment because the judge said the cops were scared and that it was OK for them to shoot up the car that didn’t match the description (Blue truck versus white / grey, different manufacturer) and contained people who didn’t match the description (Asian women versus black man).
It gets even BETTERER though. That wasn’t the only vehicle they stopped that blatantly didn’t match the description and they still used violence to stop.