Hello,
i was reading the lecture notes of Prof Oliver titled Dhammacariya and Samacariya and i thought there was a very interesting point raised on page 5 whereby he said "people do not know that they violate the second principle by keeping quiet." This was in regards to the second precept of not stealing, and the idea is that if one knows or sees someone else stealing, but does not say anything to stop it, that it would be a form of assisted stealing so to speak.
I found this interesting because a few years ago, i remember having a discussion in a dharma class with another student and the topic was on kamma. And we were discussing if we see something wrong, should we get involved or not? One of the students quite strongly said that we should not not get involved in other people's kamma.
I suppose one has to weigh the pros and cons of any situation. Things are not always so black and white and clearcut. We should try our best to adhere to high ethical standards but at the same time, we do not need to "police" other people.