some people might say they are neutral and don't want to get involved in things that don't concern them, they don't know this man and if they do something they might get hurt, besides its not like they are committing the crime or doing something bad, right?
Because you chose to stand back and watch as a crime happened while you could have helped, you've become a part of that crime, you may not have held the knife nor made the threats, but simply by standing around and watching as another person gets hurt, you become as guilty as the culprit.
Some might think that others should be able to handle their own problems, why should we defend people who cant defend themselves? Survival of the Fittest is how it works in the animal kingdom, but we're humans not animals and if you choose to ignore the needs of others, please don't expect them to help you in return, everyone has their own problems and the only way to live this life we are given is by working together and helping each other.
Don't watch others suffer when you can help them, no one deserves to be hurt.