I grew up in a sparsely populated community where there was never a place for the innocent fun of being high and/or drunk or anything else embarrassing that did not enter the social memory (permanent record) of the community. And that memory even lived a lot longer than you. The downsides of living in the global village is turning out to be the same as those of living in a small village. It would probably be worthwhile to study how small villages learn to negotiate privacy issues.

You are right that intervention in a fight has all sorts of risks but some of them are less risky than others. Calling 911 or alerting local authorities. Enlisting others to help stop it. 

Even intervening to help the poor man that fell onto the tracks of that subway would have been risky. Choosing to help him or not may have been a difficult moral choice; photographing him during and after the event was not. It was callous and cruel and jaded.

But intervening was not the only issue in the above example. The man was waving a gun around and no one noticed. What if instead of shooting a specific person, he had just opened fire on the entire car?  Being aware of what is going on around us can sometimes be simple self-preservation.

Being aware of my surroundings is very hard for me to do even without cell phones and tablets. Always has been. It is likely why I have always been accident prone. I wonder how much more dangerous it will be out there as technology increases the accident-prone population?