A few years ago there was an incident in California where some nutcase was running around inside a supermarket with a sword hacking up people. If my wife or kids were in that store and were hurt, and I found out later that there was an armed off duty federal agent that ran for the exit because he was worried about the financial aspects of intervening I think I would be extremely upset....I'm no hero, I just don't think I could live with myself if I had the means to end something like that and decided not to based on a possible civil suit later. Some things are more important than money.
On the flip side.....if I were in a bank and it was being held up..and nobody was hurt yet, I could kind of rationalize that the robber would likely just take the money and leave so I would be ok with running out the door.