That experiment is stupid in so many ways and, as you note, seems to be a pretty good way to get someone shot. Nevertheless, it certainly demonstrates the diversity in courage levels and mental acumen existing in our general population. You have the absolute cowards who simply run away, the courageous souls who join the the fray trying to help the "victim," the "politically correct" types who use their cell phones to call 911 (a lot of good that would do for a man who was about to be garroted to death), one man who empties a fire extinguisher on both "victim" and "attacker" but fails to prevent the elevator door from closing and thereby leaves the "victim" to his "fate," and one character who appears simply to be taking a video of the struggle on his smart phone.
As for me, I've got the scars of a few such encounters in the past to know that I would be jumping into the middle of that "furball." But again, such an "experiment" is a reckless thing to do and could easily result in someone being shot.
[Edited typo.]