Back to the Middle School survey question

This is really a two-fold question.
One, I think there is the bigger question of why people do or do not get involved when there is something amiss going on. I think that sometimes we have had experiences where our perceptions have been negated by others. Like I will hear from teachers that they will not interfere in bullying situations in school because they have been told in the past by students: "we were just joking around" (or something similar). Or police officers who are called in on domestic violence calls, only to have both parties turn on them or the victim defend the perpetrator. So when that happens you don't want to do anything the next time (Learning theory = avoid negative outcomes; none of us like to be told we are wrong, especially teachers and police officers :-) authority figures that they are).
Two, what do you do when you see something bad happening? I think that there is no preparation teaching us to jump into intimate situations and put ourselves at risk. It runs counter to our survival instincts. And often there is no sense of "what can I do in this situation." Personally I love having a cell phone for this reason - I can call the police and not have to put myself at risk. I see a car broken down or an accident or whatever and I can just call and feel I have done something... But if you are 10 years old and you are walking home from school and see bigger kids take some other kid's glasses, I think you have no idea (if you even have a cell phone) who to call and what to ask for. And you would have to be crazy to run over and tell them to stop (unless you hope the humour of your challenging them will cause them to collapse in laughter allowing you and the other child to run away).
And yes, it depends on the situation, and tons of dynamics, and if there are no simple answers as an adult, there certainly is no easy way to help kids.