In late '92 I pulled a guy off a woman after he attacked her because he thought, wrongly it turned out, that her son had slightly injured his daughter at a McDonald's playground. We fought. I slugged him. He stepped back, pulled a gun & pointed it at me. For some reason he didn't shoot. Instead he turned & walked away.

Police came. Interviewed me & the woman, but I don't think it was any big deal to them, so I never heard anything further from the incident.

Point being, I wouldn't do anything differently, but there can be dangers that aren't obvious.

Wrt to the train incident & bystander effect, isn't there another aspect, i.e. people base their behavior on that of others? No one else is intervening, so maybe I shouldn't? Diffuse responsibility. We base our response to a situation not only on what we see is happening, but how others respond. Of course that doesn't excuse the other passengers. This was a fail on the level of Jamie Rohrs (he's the dude who left his fiance & child behind during the Aurora Theater shooting, actully drove away, only coming back when she, assisted by a stranger, got out & called him).