The law of karma teaches that if we ignore doing something that needs doing, then we have acquired bad karma and will have to bear the consequences of 'not doing something'. If we see injustice and do not stand up against it, then we acquire bad karma. Krishna taught that we have to stand up against injustice. Where possible, we must try and find a way out without resorting to violence. For example, Gandhi was able to gain independence for India without using violence. In many cases, it is possible to resolve serious disputes without using violence.

Reference: Primary Hinduism by Seeta Lakhani (Ch.4, 'What Hindus Believe', p.53)