I think the 'pass by on the other side' reaction is also quite common. I've seen 'social experiments' on TV where someone pretends to collapse in the street, and people saunter past unheeding. I do see that one might fear it's a scam or a decoy for stealing, especially in a city environment, but it's still chilling to watch.

I've had the rare pupil who has done something strangely cruel or bizarrely bad, and most of them were unable to explain it.

Human nature is indeed complex, unpredictable and daunting...