My wife and I were discussing this "test" second-hand. We hadn't seen it, but heard a good synopsis of what happened, and we too were appalled.
This is the first time I've actually seen it.
I do see a few potential flaws with the setup here.
The main one was that the girl wasn't a very good actress, IMO, she wasn't "selling it". That perhaps created the impression that she was a bratty kid trying to create trouble, and the man was a legitamate family member or caretaker. I've got four little girls at home, two toddlers, and two crawlers, and you quickly learn to distinguish anger/frustration/whining from pain/terror. If we didn't we'd never get anything done around the house.
That girl never once set off my parental pain/terror meter with the tone of her voice. Even if you're not a parent, there's a shrill quality that enters a child's voice when they really "mean it".
She also didn't say the same thing consistently each time in front of each test subject. "You're not my Dad!" could just as esily be construed as "I'm a bratty kid, and I'm being a jerk to my stepfather..."
That's why it's important to teach your kids to yell "Stranger! Help! I don't know him!..." etc. With the divorce rate in the U.S. "You're not my Mom/Dad!" probably gets yelled by an upset child at step-parents thousands of times a day in America. If I heard the word "Stranger", I'd definitely intervene, even at the risk of doing so at the behest of a bratty child who was faking it.
I doub't that the passers-by knew this, but it's also true that something like 95% of all child abductions are non-custodial parent disputes. Even once is too many, but a very, very, very, small percentage of child abductions are true stranger kidnappings, murder-rapes, or child molesters. In a country of 300 million plus people, it's still rare, and that's why the cases that do happen make the news in a big way. When you add in the number of children who are runaways, the percentage is even lower.
Despite all that, I agree it's still disturbing, however perhaps not quite as disturbing after seeing the NBC setup for myself, and the quality of performance.
I also found it striking that the men who did help seemed to have more of a "urban minority" background than the white passers-by. (It's also my impression that the minivan driver stepped in because he had some "group authority" to act, as he saw the other two men already on approach...)
It could just be the dynamic of two men being more willing to act, as there's the whole aspect of shared-responsibility, and possibly even an undercurrent of reinforced machismo. I don't believe I ever saw a pair of individuals travelling together, other than parent/child in the test.
Aside from that, and I admit it's complete wild conjecture (and potentialy very unfair stereotyping) on my part, but part of me can't help but wonder if it's because thier minority upbringing sensitized them to the "reality" of the possiblity of crime, whereas the whites were more likely to have a natural state of denial. They're less likely to directly experiance or witness crime, therefore it dosen't "happen" in thier worldview. Whereas two young black men might more readily posess a visceral understanding that things do indeed "go down".
I find that dynamic eerily similar to the "denial" plank in the anti-gun platform. "It'll never happen, (here, to you, to me, etc.) so you don't need a gun.." etc.