[laylo]

I studied this phenomenon (bystander intervention) in social psych.

The main issue is not that people are scared of being hurt, or even diffusion of responsibililty ("Someone else will help."), but that they are afraid of being wrong in front of other people. If someone needs help and the bystander is alone, (s)he will be much more likely to help than if others are watching. Also people are totally unaware of the effect when it is happening. It's easy to say "If that had been me I would've definitely done something", but the behavior is VERY consistent among the studies done, and the only group that seems immune is children. The only real way to fight it is to become aware of it.

ETA: If you ever need someone to intervene for you and you're among a crowd, the most effective thing to do is to look one person in the eye and ask him or her specifically to help you.