That's true but it also kinda acts as an example as what has happened throughout history. For example if you look at the soldiers in the germany during the holocaust. That is just one example, looking throughout history there is a lot more.
I understand that I couldn't use any of these examples as hard evidence, but I just thought that it was interesting to the idea that an officer is seen as an impartial witness.
He is often seen as impartial because he does not have any real skin in the game. Win or lose, he has no stake in the outcome. The officer gets paid the same either way.
As for who gets into law enforcement, your contention that people get into police work are seemingly borderline psychopaths is ... well ... truly ignorant. I have never met ANYONE who got into the career to screw with people! Not to mention the fact that a background and psych evaluation would almost certainly weed such a person out before he had such an opportunity. Even if one did sneak in, it would probably not take long for such sociopathic tendencies to come to the surface resulting in discipline or termination.
And, as for comparing driving on the autobahn compared to the US is apples and oranges. Americans would not put up with the requirements for licensing and driving, and the draconian penalties for offenses that are present in most of Europe compared to the US. They tend to take driving seriously ... here in the US we give licenses to people that are minimally qualified, young, and almost never subject to re-testing.
Finally, while traffic fines might bring the government a lot of money, at least in CA (where this discussion began) the police make almost nothing on moving violations. There is no financial incentive for the police to issue citations.