What I've found is that when one person breaks with "the group conformity" by acting in a considerate way, a kind of domino effect can happen, and others do the same. For example when it comes to offering seats on crowded trains. Not always, but quite often. The group dynamic is, for a moment, changed.

People may look as if they are frozen into immobility, but sometimes the ice can shatter. It's a kind of catalytic process.