I think though that is entirely the point - people are saying in advance how they would behave and I would expect most/all people to say they would try to help but obviously when it actually happens reactions can be unexpected.
I have also been involved in a gunpoint situation when working in a summer job from uni - I froze, as did 2 of the other people. I don't know how I would have reacted if I was alone. I have been mugged twice as well and well what can you do. OTOH I have stepped in, in some violent situations, and also walked out into traffic because a bus hadn't seen a kid but he would see me.
So yes I know exactly what you mean. But until it happens you don't know what you will do - and when it happens what you do might not be what you expect. There are so many elements - who you're with, who else is there, bystander syndrome, how you are feeling and so on.
But for people who are not in that situation to say in advance, nope not interested wouldn't help, I find that unusual.
Oh just seen you think there is such a thing as "superhuman mummy strength". What about fathers, what about other relatives, what about strangers? That man who went into the factory in Bangladesh and rescued scores of people, at huge risk to himself, that was a good thing, no? On the tubes in London, when they were bombed, I knew a couple of people caught up in it, others helped them, that is good, right? Surely we would all hope to help a person in need? For someone to help us if we were in need? Although of course when it happens we all react how we react and that is the way it goes. But to say beforehand, in the safety of your home, no I definitely wouldn't help, not interested, nothing to do with me. i find that very cold and unsettling and it makes me shaky.