Individual humans are - on average - empathic, brave, and rather surprisingly clever. Large groups of social primates, on the other hand, are capable of cruelties so depraved the contemplation of which threatens to break the mind.

As I believe pointed out by Tommy Lee Jones in _Men in Black_, somewhat more succinctly.

The really poisonous aspect is how individual empathy in social groups can incite even greater violence, so as to reassure the group that you're all on board with atrocity lest you become another target for it. Diaries of German soldiers on the Eastern Front relay this. Also the stereotype of the ex-prisoner camp guard who is more cruel than the actual occupiers - Ukrainian/Baltics SS were particularly monstrous. Samuel Jackson's character in _Django Unchained_.