Getting involved in a violent event is a personal moral decision, and I respect your decision. Each person would have to make up their own decision on this. I personally would never get involved, unless it is absolutely 100 percent clear to me who the bad guy is and the victim is a true defenseless innocent. For me, that is pretty much limited to a child in mortal danger. If the person being attacked is an adult stranger, I'm not going to risk my own life for them, and that's my moral decision. First, I'll never be 100% certain that shooting victim is truly innocent, even if it's a store clerk or a 100 pound woman. For all I know, the clerk or the woman was selling drugs on the side and the shooter is exacting revenge for a deal gone bad. Second, that person is old enough to take responsibility to prepare for their own defense and protection, not me. I'm a sheepdog for my family, not another flock.
Concerning the Warsaw ghetto scenario. That's just a plain no-win situation and you will be shot dead. Better to live, prepare and fight back smarter another day.