The vast majority of people, when in that situation, will not try to help--especially if the threat is only potential, especially if there's a number of people that "should" interfere and it's not their "responsibility." I've always just assumed it was a quirk of human psychology--I think there's a word for it. I never really wanted to delve into people's justifications for inaction. >___>

And most of the cops I know are racist--but more in an offensively ignorant "Man, all the natives ever do is fucking drink!" kinda way, not in a KKK kind of way...