Outsider:  The question of when to become involved in "other people's business" is a tough one.  Should you, out of fear, indifference or whatever, stand by, observe and "ignore" someone abusing another person?  As an individual what is or is not "your business"?  If someone is physically attacking and abusing another person, should you turn away, hurry on by, and pretend you didn't see it? or Should you intercede in an effort to help the victim?  I think it's far too cavalier to just dismiss such a choice as involving a PC action.  

Police officers often will state that domestic disturbances rate among the most dangerous circumstances they face, and it's quite understandabled that individuals hesitate to become personally involved.  It's a tough question.  What do YOU think people should do when witnessing such an incident?