As someone who was ticketed for going the speed limit on a bright sunny day on a rural highway with no other cars around, where the cop wrote down two different speeds and it just happened to be the last day of the month... I assure you it is not always objective. Cost me 5x to fight it what the ticket would have been, but it's the principle of the matter.
I'm not discounting this issue. I'm sure it happens but: 1. having a speed limit allows you to know the cop was objectively wrong (barring broken speedometer). 2. Imagine the leeway cops would have if they had the discretion in determining "dangerous driving". The abuse would be even worse.
