I just hate feeling helpless watching stuff happen to people

Becoming an additional victim does not help anybody. In fact, quite the opposite is true. It might divert attention from the original victim and even delay help.

Standing and watching is not the same as calling for help. By being an observant bystander and relaying important information to the relevant people you are making yourself invaluable. You can tell the police exactly what is happening, where, by whom, descriptions of people involved, and then if willing be an independent witness in the case. This could be especially important in things such as domestic violence where the victim refuses to cooperate with Police, yet an independent witness can secure a prosecution