Not to take away from the OP's experience
But theres a guy my dad knows quite well (he sold me my first car!) who is in his 60's and well respected in the community who intervened when he saw a domestic situation on the street. He ended up in an induced coma in intensive care for several weeks and now cant leave his house
Months on because of the trauma.
People do have a duty i believe. But i think that duty is to call the authorities. Not to put themselves in danger.