Police in the US are very much not like police in other Anglo countries; they are much more adversarial.
Not to say the other police are perfect, but it seems much worse in the US. Example: I'm from Australia, and was recounting a story here on HN about how I don't like that subtle power play when police pull you over and talk down to you in the car. So I get out (I'm very tall) and wait for them in a friendly manner. It changes the tone of the traffic stop. Doesn't change the outcome, but it's hard for them to talk down to someone they have to physically look up to.
On relaying this story, multiple HN'ers from the US thought I was genuinely putting my life at risk of being shot by the police, and told me I should never ever do that. This is a genuinely foreign concept to me - that I should be fearful that police might be predisposed to shooting me for getting out of the car. That these folks even have that general fear speaks volumes as to the excessive force the US police use.