Crowds tend to get a lot of bad press, and they also tend to be treated as pathological in the social sciences. We are at our best, it is often assumed, when we act as individuals. Crowds, on the other hand, bring about "the diffusion of responsibility."
This is one explanation for why a group of New Yorkers would stand idly by on a subway platform and not help a man who is stuck on the tracks and about to be killed by an oncoming subway. This is a disturbing psychological condition to contend with, but it may not hold true.
Recent research using data and virtual reality tests suggest that we can actually be at our best when we are part of a crowd, even when our own well-being is threatened.