At what age (tweens upwards) do you think it would be at all useful to show images or footage of distressing or traumatising subjects, whether contemporary (eg footage of man being run down by police after he had stabbed people and then man being shot) or historical (eg drawings of how slaves were physically punished). Also when talking about "fake news" showing really grim images or footage instead of using less grim examples.
Whenever I hear about this happening in class at school I just think "why..." - subjects are important, but imagery and footage not so much. One of dc's teachers seems to have entrenched ideas about how it is good for tweens/teens to see grimness.